Hi there Amy..
I think you are spot on...it does seem to be an allergy
of sorts & if i were to hazzard a further guess, it is most likely a photoallergic dermatoses!
However, Dermatology is a visual line & as such, one would prefer a clear digital image of the lesion & you may upload it on this site using the upload data icon to the right of your screen.
To get rid of it, please do use a sunscreen of SPF 50 in the mornings from dawn till dusk & a hydrocortisone cream
in the evenings daily for 3-5 days coupled with an antihistamine eg 180mg fexofenadine
taken orally & this should allay your symptoms.
However, one has to isolate the allergen & this may take awhile. Patch & prick tests with photoallergic testing are available in larger hospitals with a good dermatology department & this will help pinpoint the cause.
Good Luck & Godspeed!
Dr Praveen Rodrigues MD