I would also say hand, foot, mouth. I recently had this (at age 23) and I only developed sores in my throat (thought it was strep). Although called hand, foot, mouth it does not mean sores will appear on all three, but they can. Also, the cold like symptoms are very typical of this illness. Being an active and retaining normal activities while having sores and cold like symptoms is also very common. I wouldn't rule this out just yet, but you may be right, it may be a food allergy. Perhaps you can visit your family doctor...he/she can give you "magic mouthwash" to dull the pain, but that's basically all they do.
P.S. WASH YOUR HANDS OFTEN, this is extremely contagious!