My 12-week old kitten, help

Hello, I just got my 12 week old kitten. I got him 3 days ago. The first day, he was fine, running all over the place, etc. Yesterday & today he just seems to sleep all the time and won't really jump everywhere like he did before. He seems more docile. Could anything be wrong with him? He did get a Fel-O-Vax vaccine and wormed.

Lots of times cats are a bit drowsy after getting shots.
You might want to give your vet a call tomorrow. Is he eating and drinking water??

I agree, it's probably the shots. One of my kitties slept practically nonstop for a day and a half after getting her last set. She perked back up to her bouncy self in a couple days though. Congrats on your new kitty!

My kitten was lethargic and off his food (he still ate, but not as much as usual) for 24-36 hours after each set of vaccines. What you describe sounds quite normal, but if he doesn't have more energy in the morning I'd ring the vet to be on the safe side.