C.
I'll second the L-Lysine suggestion. My mom always had horrible canker sores...they would cover her whole mouth and go up into her nasal passage...awful. Anyway, she would take L-Lysine at the onset and they would go away. She got to the point where she just took it every day for many years, and she hasn't had a severe outbreak since. She still gets one every once in a while, and then just takes L-Lysine and uses Abreva topically. She also claims taking a daily sauna helps, but I don't know how practical that is for everyone! Good luck!