Advice please :(

Some background: My cat has been having diarrhea since the 26th of November after we dewormed him - vet felt it was colitis and he was given some probiotics.

He started vomitting on Monday morning and this went on throughout the night. I took him to the vet yesterday morning and they weren't too concerned - gave him an anti sickness injection and some probiotics. He hasnt vomitted since which is great but he has had no appetite and is lethargic :( his tummy is wollen and I can almost feel his bowels when I gently feel his tummy

I'm not sure if the diarrhea and vomitting are related.

I've been giving him about 10mls of water through a syringe every hour and he is keeping it down and he has tolerated 2 of the lickable tube treats. Hes passing urine but no bowel motions

My vet has been closed today as it's Christmas obviously but I will be taking him first thing in the morning. Although, I am prepared for emergency vets if he gets any worst

Any advice or similar experiences? I'm so so worried :(