Think outside of the box, too - it could be as simple as a new
lip balm or a food, but could also be another medication you might have just started using, a soap, shaving cream (if you're male), etc. Antivirals help a lot, but they can't override everything. I've had hsv2 for 15+ years, and acyclovir works wonderfully, but if I get a cold or the flu, forget it.
Hope you feel better soon!