Hi Lyndal, Welcome to HealthcareMagic Forum.
Your symptoms suggest, you are having Herpes Labialis, Did you had fever
recently? How old are you? Herpes labialis is infection of the lips, mouth, or gums with the herpes simplex
virus. Kindly get yourself examined by a Dermatologist
so that he can evaluate you completely and rule out the exact cause. Tzanck test of the skin lesion may confirm the herpes simplex virus. If left untreated, the blisters will disappear in a week or two. Antiviral
medications taken orally and applied topically may help the symptoms go away soon and decrease pain if you have any. Wash blisters gently with soap and water to reduce the spread of the virus to other areas of skin.
Wish you Good Health, Take Care.