3 year old is sick. I'm worried help!

Monty our 3 year old got his second distemper shot Friday and he seemed fine. A little hot, but he's got quite a bit of hair and we unfortunately don't have air conditioning and it's over 89 out. We've kept the fans running and windows open for him and our two year old cat as well Monty has seemed tired but fine. But today he vomited a hairball. Doesn't seem to want to eat or drink or move. Then just now I went upstairs and he pooped a little on the floor before making it to his litter box. It was pretty bad diarrhea. Smelled very bad and he had to be washed off it was all over him. I don't know if it's just the heat and he'll be ok or if it's something more serious. When is it time to call the vet?

It could be a reaction to the vaccine.  Usually the rabies vaccine is the one that causes a reaction but any vaccine can cause one.  If he isn't eating by tomorrow I would get him to a vet even though it means an e vet.  Sometimes allergic reactions can spiral into something pretty nasty and treatment is needed to bring them out of it.