Nurse nurse nurse!
My two boys are the same--diarrhea, vomiting, liquid diet, diaper rash, you name it! It was horrible!!!!
Anyway--my kids were willing to eat soft foods, not just milk, so we did popsicles (not healthy, but at least liquids that is not milk), yogurt, ice cream, applesauce...yep, that all gave him more diarrhea, but at least I knew it was from teething. It was summer, also, and we were on my inlaws farm, so I let him go nakey outside (the diarrhea wasn't THAT frequent; we just sent him out after he'd had a BM).
My kids didn't necessarily throw up from the food they ate; they threw up because of the teething--I think they were actually bored from eating such bland food. Then again, I didn't really want them vomiting spaghetti or blueberries. Will he eat baby food? Mashed bananas?
Remember, though, that's one of the blessings of nursing this far; you CAN just nurse him and he'll be fine. I think with my oldest it lasted about 2 weeks and then they came in (the symptoms weren't that frequent; he was just in pain that long); my youngest it was much shorter. So...hopefully it's on the way to being DONE!