Puppy is shaking ?!?!

So this is something different that I wanted to ask to see if anyone has had a similar experience. My puppy is a little over 3 months but has been sick for the past week. We took him to the vet last Thursday after we noticed he had been getting worse for 3 days. They told us he had parasites and he stayed 4 days at the vet and came home on Sunday. 2 days after coming home, he still does not seem himself and hasn’t gotten better. I took him back to the vet today just for reassurance. He has been eating but not too much, has been pooping a few times a day, and has not been drinking water no matter how hard I try. The vet prescribed him more medicine/vitamins (8 total). I had to give him 5 of them an hour ago. I asked the vet if it’s okay to mix all these meds and he said yes. However, as I was just about to leave the house for 4 hours...my puppy started shaking. Not a I’m scared shaking but more like a muscle spasm shaking. It didn’t seem like a seizure as he was conscious and alert. It was pretty much his whole body spasming. I called the vet right away and the nurse said I could bring him in tonight or tomorrow morning. I decided tomorrow morning, but now I’m scared. My mom has said that maybe he’s just too sick and too far gone, yet the vet didn’t seem totally concerned today, just concerned that he lost weight and that he’s not absorbing nutrients. I really wish I could attach a video onto here but can’t. Has anyone had this happen to their dog? He ate pretty well right after I gave him the meds. I’m thinking it could be a reaction to the drugs...like how some people get jittery when they take certain meds. I’ll be taking him to the vet first thing in the morning. But for now I just need to ease my mind. I felt horrible leaving him for 4 hours today, but I really didn’t have a choice.