Cat vomiting - plus other health issues

Hello, I am new to this site (posting to it, at least, I have been lurking for quite a while). He is going through some health issues recently and I just thought I would ask for some advice because we have been back and forth to the vet quite a bit. The main problem I have right now is that he is vomiting after he eats.

Some backstory: Jack has had a pretty bad cough going on for a few weeks now - it progressed from a dry, wheezing cough to a very mucous sounding cough. I brought him to the vet where he had x-rays, plus his general wellness check up done. While I hadn't initially gotten the report for the x-ray, I was told that his urinalysis came back with bacteria in his urine so we started him on clavamox. Two days into clavamox he started vomiting, so I brought him back to the vet yesterday and we have discontinued taking it. We decided instead to go with an injectable antibiotic, plus an injectable anti nausea and probiotic packets to sprinkle on his food. At the same time I heard back about the x-ray - doctor said it looked mostly normal, but "a little fluffy" and may be seasonal allergies and told me to give me 1/2 a benadryl tab 2x/day. Meanwhile, over the past several weeks I have been transitioning my cats to eat more wet food because 1. I learned 100% dry food is not the best diet for cats and 2. Jack has had some issues with crystals in his urine (all cleared up now thanks to added wet food and a water fountain).

Back to what's going on now -

- we had vomiting and loss of appetite with the clavamox, so stopped the clavamox - got injectable instead

- started giving my cats food at designated feeding times instead of free feed kibble + wet food (though still include both kibble and wet food) because jack needs his probiotics added to his food equalling 1 packet/day

-giving Jack 1/2 benadryl tab last night and this morning

Last night went okay, Jack ate alright (he never eats as much as my other cat (Luna) in one sitting) so it was nothing really abnormal, though I wish he would eat more. This morning, again - went okay, still didn't eat as much as I'd like. I got a text while I was at school from my roommate that Jack had thrown up. Not really necessarily regurgitation type vomit, more liquid. Came home and cats were crying for food, fed Jack some wet food only with probiotic sprinkled on top, ate about 1/4 of it and immediately regurgitated. Jack has always had issues with scarf and barfing when free fed kibble, I had actually recently bought a timed auto feeder to cut down on that and it really has, but he has started up again but the difference is that he is not really eating. I know it is very dangerous for cats to go without food because of fatty liver disease and I am worried that he is throwing up after just about every meal. 

Could the clavamox still be in his system and making his tummy upset, even though it's been more than 24 hours since I've given him any?

Could it be the banadryl or the probiotics that are upsetting his stomach? I hate to keep bringing him back to the vet because it's so stressful and my other cat Luna always gets really upset when he comes back (hissing at him and swatting if he gets too close).

Could it be the wet food that is the problem? He has been eating wet for a while now as a supplementation of his dry food, but I have been increasing the amount of wet and decreasing the dry, plus I don't always get the same brand or flavor of cat food (he is also VERY picky about the wet food that he will eat, so I often have to buy new kinds when he has stopped eating one flavor and I often mix some of his dry food in with it because he loves the kibble).

Any insight would be greatly appreciated! I am going to try to just feed him so dry tonight without any supplements or other medications to see how he does because he has only regurgitated dry food when he has eaten too much too quickly (and sometimes he'll just eat it right back up). I'm just so worried about my poor guy, he's had so many vet visits in the last few months, it breaks my heart 

What kind of probiotics are you using? They are not all the same. Purina's Floriforta is basically worthless as a probiotic, because it only contains one very minor strain. Generally you want something with a high amount of L. acidophillus, and bifidus is also good. It doesn't have to be a pet-formulated probiotic, although there are some options. I've used Pet Ultimates probiotics and they worked well, but I switched to PB8 acidophillus because it's much cheaper and it works wonderfully for my cat. I sprinkle half a capsule on her food twice a day.

I don't know a lot about causes of cat vomit. My cat's problems have been mostly on the other end of the digestive system. But she did once decide she wasn't going to eat a certain flavor of food, and she went about a day and a half without eating and I think that threw her system out of whack because when she did eat she started throwing up. So instead I basically poured some of the probiotics from a capsule straight into her mouth without any food. She actually enjoyed it, because she doesn't mind the taste and she was hungry, so she was trying to eat the gelatin capsule while I did it and I managed to get her to consume a good bit of it. Then I waited half an hour to give the probiotics time to get ahead, and then fed her some food. She stopped throwing up, and I fed her the probiotics like that ahead of meals for a few more days and she was back to normal. 

Based on the sequence of events, it sounds like the antibiotics-both the clavamox and maybe also the shot-disrupted his natural microbiome and it hasn't returned to normal, maybe because the probiotics you're using aren't very effective. For reference, this is the exact bottle that I used to solve my cat's vomiting: http://www.vitacost.com/nutrition-now-pb-8-pro-biotic-acidophilus-for-life-14-billion-120-capsules. I usually give her one capsule a day split into two meals, but for the vomiting incident I gave her an entire capsule before each meal. 

there's no reason a medication can't keep upsetting your cat's - or anyone's - stomach for over 24 hours.  our cat recently had unpleasant side effects from a flea treatment pill (capstar), and although technically the pill lasts 24 hours, it lasted over 48 for HK (we could tell because the fleas kept dying), and his loss of appetite lasted for over 5 days.

btw, anything can upset anyone's stomach even if it usually doesn't for most.

hopefully cutting out everything will help.  please let us know how he's doing. 

Thanks for the replies! The probiotic I am using is called Advita and I got it from my vet. 

Ingredients: 

Dried poultry liver, dried Enterococcus faecium fermentation product, dried Lactobacillus acidophilus fermentation product, dried Lactobacillus casei fermentation product, dried Bacillus coagulans fermentation product, maltodextrin, dicalcium phosphate, silicon dioxide, salt, inulin, ascorbic acid, vitamin A acetate, vitamin E supplement, zinc proteinate, manganese proteinate, ferrous sulfate, copper proteinate, and sodium selenite

I gave him some dry food last night and this morning and so far he has kept it down. Next I am going to try to give him the probiotic and then if he's still doing okay give him the benadryl and see if he continues to do okay. I also got a prescription card for Hills Feline I/D - has anyone ever used this? My vet said only to use it if he continues to have problems, I really hate these prescription cat foods as I like to feed my cats grain free low filler cat food and the prescription foods are basically the opposite of that.