Anyone have experience with your child having many mouth ulcers at once?

My 2 year old has a virus, possibly hf&m disease but since he is not breaking out on his hands and feet, they are thinking it is probably the cold sore virus making its first appearance. I am devastated for him. He has had nearly nothing to eat in three days and can only drink. There are about a dozen ulcers in his mouth, on his tongue and gums. I went back to the doctor concerned about him not eating and she said it is okay as long as he is drinking. But for how long? What can I do to help him? He wont eat anything I try to give him. I have the bennadryl malox lydocane mixture but it is not helping. Ugh I just wish it would end and I am desperate for my son to eat. Should I get another dr? His long would you let your child go without eating (but drinking fine) before you demanded they hospitalize them?