I'm so glad you took him to the dr, I didn't post but my money was on an infection lurking somewhere too. I hope he's feeling much better soon.

ETA - don't waste your energy on feeling guilty. You did the right thing and took him to the dr once you knew it was a possiblity and that's the main thing. BTW they often check a few days later with the little ones because sometimes the ABs need tweaking, the important thing is that' you're onto it now and he can get better.