Have pain in throat. Took antibiotics but no use. What could it be?

My boyfriend got sick a week ago with an on and off fever and huge white spots in his throat. He couldn't swallow without an immense amount of pain, and while he tested negative for Strep Throat, they told him he had a bacterial infection and put him on five days of antibiotics. He began taking those on Monday, and started feeling better Wednesday, and was back to himself by midday Thursday. The antibiotics ran out on Friday, and he felt fine all weekend up until today. When he woke up, he knew that whatever he had was back; he has white spots again and cannot swallow.
I find it a little odd that in kissing him right before he was sick, and in between when he felt better and now, that I haven't gotten whatever this is.
What else could it be?
(He also asked me if it could be something to do with him going down on me on Sunday. I don't think that it's a possibility, but is there any way that that made him sick?)