I suppose it is possible your symptoms are due to recurrent
herpes, but I doubt it. Recurrent HSV outbreaks rarely produce fatigue, headache, or lymph node swelling, and back pain is rarely associated with herpes at all. And although recurrent outbreaks can occur while taking valacyclovir, they are rare -- and monthly is unheard of. It is possible your HSV has become resistant to the drug, but that's quite rare as well.
As for valacyclovir side effects, you needn't worry.