What should i use on severely sun burnt lips that seem to have broken out into cold sore blisters.

Oral herpes: Oral herpes (cold sores) is often triggered by sunburn. If you have a past history of oral herpes and are pretty sure that's the problem, contact your doctor ASAP for a prescription of valacyclovir, which will speed healing. A single oral dose (2 grams) is all you need. Do it immediately: waiting even a day or two markedly reduces effectiveness. Don't use any creams or ointments; none work well.