Help..My 12 week old kitten can't keep his food down.

Hello..I'm new to this site and also new to cat ownership.  I have a 12 week old bengal kitten named Roman and a year old morkie named Niko.  Roman is basically my first cat.  My roommate has had several but she is out of town.

I've been having issues with roman and niko eating each others food.  I feed them in separate rooms at the same time but roman always comes to niko's bowl.  Niko eats pretty freely when he pleases so there is usually always food in his bowl.  Niko ate Blue Buffalo Wilderness canned wet of various flavors and dry food as well.  Roman ate blue buffalo wilderness Kitten wet and dry.  Both of them have 2 food bowls..One is always full of dry food and I feed them a can of the wet a day. 

Recently I've done some research and decided to switch them to Wellness Core or EVO innova.  I couldnt find the evo so I opted for the wellness.  I made the gradual switch this week and niko and roman both seem to like the taste of wellness core.  This morning I heard roman crying in pain than he began heaving and threw up.  He did this twice more during the day...In addition he was acting very out of character.  Non-playful, non-affectionate...He loves to play and sleep with niko.  Now he was acting lethargic and seemed to just want to be alone.  I decided in the evening to take him to the pet hospital.  After the exam the vet suggested x-rays because she felt something hard in his stomach.  She said his blood work and vitals were normal.  The x-ray revealed constipation but no other blockage.  They gave him fluids for dehydration and some meds for nausea then 3 hours later he was discharged. 

Now I'm back at home and he is acting a better.  When we got home the first thing he did was a huge poop.  Now I'm thinking if constipation was the issue he is better.  I give him some food after he uses the bathroom and he eats all of it.  An hour later he is heaving and throwing up again!!!  Its a dark bile with food in it and its very strong smelling.  Do I need to give the situation more time?  Or should I take him back to the doctor? Any suggestions on how to make him feel better?  I switched back to his old food BTW.

Thanks in advance for your help.

Here are some pics of roman and niko

Was he treated for worms?  That's one thing to consider.  Also, the dog food may also be doing a number on him.

The grain-free food might be too rich for him.  What were you feeding him previously?  Was it wet or dry?  If you just switched this week to the dry, you'll probably need to do it much more slowly.  The sudden switch may have thrown his system off.  Are you feeding him a kitten food or adult food?

Do you possibly have any plain meat baby food on hand?  He might be able to tolerate that.  You could also boil a piece of chicken in unseasoned water and shred some of it.  Then add in some of the broth to make it the consistency of oatmeal and offer that to him.  If nothing else, you could take up his food and leave the water for him overnight.  In the morning, try feeding him again.

Hi...His food is kitten food.  He has only had grain-free food since I've gotten him.  The difference is the other is wilderness now he is on wellness core.  I've switched it back for now.  I dont have baby food but I can get some now.  Thanks for the suggestion.

When you get a new kitten you shouldn't change it's diet for a couple of weeks, and then only gradually.  Sudden changes are one way to giving a kitten an upset tummy.  If he came from a reputable breeder he should have been wormed but it's another avenue worth investigating.

BTW what is a Morkie?

A morkie also known as a yorktese is a maltese, yorkshire terrier designer hybrid.

http://www.dogbreedinfo.com/yorktese.htm

Just an update...He seems to be much better today.  I gave him some tuna juice until so he wouldn't be hungry.  Also he has eaten today and kept it down so far.  He is back to being playful..just not as much but that is understandable.  I probably over reacted..LOL.  Thanks for your help and I'll update soon.

How is he doing since you switched him back to the old food?