Depressed or too many Pit'r Pats?

For those of you who dont know Toussaint and Beasley where neutered and spayed last Friday. Since then I had separated them for a couple of days, then they were together for less than a day, then separated again after Tousse kept trying to mount Beasley. I took Tousse to the vet on Wednesday because he just didnt seem to be acting like his usual vibrant self. Beasley seems to be ok but she looks a little skinny to me. Okay, the vet examined Tousse and said there was nothing wrong with him. His vitals were all normal. Okay, if there is nothing wrong with him physically, what is wrong with my boy. Beasley and him are no longer separated but he doesnt seem interested in playing. It's raining but I dont think that could be it. He threw up today but I dont know if it was because I gave him too many Pit'r Pat (insert sheepish face here) I wasnt paying attention and left the tin on my bed and he ate the entire tin. Sighs. Sorry, I know information overload but I worry that I injured him some kind of way getting him neutered. Somebody, anybody please advise. And I will be taking them both to a different vet tomorrow for a second opinion. Better safe than sorry. I just wanted to know if anyone had a boy cat that reacted badly to being neutered. The way he is acting seems like he is depressed.