Hello. Thank you for writing to us at healthcaremagic I would suggest a possibility of herpes labialis/ cold sores. It is a viral infection cause by Hsv type 1 virus. The lesions in cold sores usually present as grouped, fluid filled lesions/ blisters on labial mucosa or neighboring skin. Sun exposure/ sun burn may precipitate/ trigger an episode of cold sore. It is a common trigger. Other triggering factors are fever, menstural cycle in females. I suggest you to visit a dermatologist for a confirmatory diagnosis and appropriate treatment. Treatment of confirmed cold sores is with Oral antivirals e.g acyclovir or valacyclovir for a week. Topically you may use an OTC topical antibacterial e.g 2% mupirocin ointment, twice daily. Regards