How long do sun blisters last on your lips, also is it possible that this is not caused by the herpes virus?

"Sun blisters"? What do you mean by "sun blisters"?. Blistering could occur with sunburn. With heavy sweating, some people get miliaria (sweat blisters) when sweat builds up under blocked pores. And sun exposure can trigger oral herpes outbreaks. If you have a history of recurrent oral herpes and the current problem is similar, probably that's what it is. See a doctor if you remain uncertain or concerned.