Male Cat - Potential urine block but still peeing - advice please!

Hello all- I am new to the site. My boyfriend and i have a rescued approximately 2 year old male tabby cat, Tito. He is such a sweetie.

About a week ago, he had an accident on my down comforter. There was A LOT of pee and he's never had an accident before. I wasn't sure what was going on but chalked it up to my down comforter being out of my duvet and smelling like my brother's pets.

Then Monday morning he was sitting in a laundry basket of towels straining to pee. When he got out, there was probably 3 drops the size of 50 cent pieces.

He was still acting very normal, running around, purring, etc. However now I was worried. He was constantly licking his crotch and I realized he was spending a lot of time in the litter box. 

Tuesday I took him to the vet who took a urine sample (I had no idea they could make cats pee voluntarily like that). Gave me Calvamox and Hills S/D food. 

I have been mixing the wet food with a little water. He is not super interested in the dry food although he nibbles on it a bit. He has drank a little water out of his bowl. 

He is still  peeing but it is small amounts. Yesterday there was probably 4-5 quarter size amounts when I got home from work. Between 5pm and 10pm, there was 2-3 50 cent piece size amounts. Now i got worried because from last night to this morning, only 2 small amounts (smaller than a quarter) but since I have given him meds and water this morning, he has peed twice and they are larger like golf ball sized.

I have read a lot on the internet about blockages and my vet counseled me on the surgery with the catheder. I will be calling my vet once they open to see if his urine sample came back and indicated anything (that is the only sample he took).

We have plans to go back to the vet Monday. However when is this considered an emergency? When he stops peeing entirely? Are these small amounts still showing a good sign? My vet hoped the special food would help him as it claims to dissolve crystals.

Thank you!

Also, I wanted to add- he has been very active and acting like his normal self (playing with toys, jumping up into the window, etc). He has maybe been a bit more vocal but he is a pretty vocal cat as it is. There has been so growling or hissing. When I try to touch his belly, he will swat my hand away.

If he stops peeing entirely or runs to the box and nothing comes out, that's when it's an emergency, as long as he's moving some urine that's a good thing. If he likes tuna get some tuna and put the juice in a bowl and add some filtered water and give that to him to help increase his water intake. If this was my cat I would take him off all dry food and put him on a 100% wet diet. I personally don't like any RX foods, and if your cat wont' eat it there's no point in using it. Here's a list of some good wet foods. You can get some of these a Petco or the rest you could find a good local pet stores. Most of the time urinary blockages are caused by feeding a kibble only diet, which is dehydrating, and you can prevent these in the future by feeding wet food. 

http://www.naturalcatcareblog.com/2010/12/the-7-best-natural-commercial-cat-foods-so-far/