My son experienced a variation of this in January - he was also one at that point (his was diagnosed as Herpangina - same virus, but sores are only in the mouth, not on the hands/feet - oh, and despite the name, it is not related to Herpes).
It was absolutely horrible. He had a very high temp that ran for days...the sores in his mouth...he didn't want to eat, drink or do much of anything. He really just laid around for almost a week - it was pitiful (and he is generally a very active boy!). There are two links which are very informative, I will include them below.
They recommend to not give them juice or pop (irritates the mouth with the acid). They say cold milk products are best (cold milk, ice cream, yogurt)....my son has an allergy to milk, which posed issues for us - but ice cream would be worth you trying.
We alternated the Tylenol and Motrin - although this experience caused my son, who was always an excellent medicine taker, to HATE medicine. :( A nurse at our pediatricians suggested to mix 1/2 tsp Maalox with 1/2 tsp Benadryl and let him swish and spit (worked for us because he spit out medicine anyways and then learned to think of this as a game!) - she also said it's okay if he did swallow it (and recommended we do it about every 4 hours...we did not wake him up at night for this, though!). Dixie cups worked great for this. It helps coat the sores. My poor son's gums were so swollen and would start bleeding - this rinse seemed to help his mouth feel a bit better, but then again it could've just run it's course. Who knows...I was willing to try anything.
Here are the links. I hope your baby is feeling better soon.
http://www.nlm.nih.gov/medlineplus/ency/article/000969.htm
http://www.nlm.nih.gov/medlineplus/ency/article/000965.htm