I too wondered about hand foot and mouth.
That said...when my first son got his 1 year molars, we were at my inlaw's house. My son started getting an off and on fever; it was hard to tell, though, because it was 100+ degrees outside. Then he got a rash all over his belly. Then he stopped eating solids, and started eating only milk, ice cream, and yogurt. Then, because he was eating mostly liquids and still spitting up at 13 months, he would spit up/throw up. Then he got diarrhea (from all the dairy). Then he got diaper rashes. After a bit over a week of all this going on, wondering what on EARTH was wrong with my son, he popped two molars and was fine. We went through the same thing for his other two one year molars. It IS possible for kids to be a mess when they teethe, but those sores in his mouth sound like a concern.