Small, weird disappearing and reappearing arm rash?

a few months ago i saw a small, scaly patch of skin on my lower shoulder. it was about the size of a thumb fingerprint. i thought i must've scd myself or something, and it went away about 4 days later. but before it went away completely, it got rougher and had the appearance of a red hickey. now i've seen it again - it developed yesterday. it was in its original state, and now it's in its 'hickey' form, again. do you have any ideas about what it could be? i'm only 14 so i'm definately hoping it's not skin cancer, such as carsinoma, but i don't want to just ignore it. sorry if i grossed you guys out! i'm just scared :'(