Hello, I seem to get a cold sore in or on my nose, sometimes onto the upper lip, once a month. It used to coincide with my period, and now it seems to have moved into the middle of my cycle. This month, however, I think it has lasted quite a long time. I have taken Acyclovir in the past with some success. Do you know the reason they recur in this way? Can I take Acyclovir or another drug as a prophylactic to prevent them? Thanks for your help!