I Started Getting A Red Itchy Welt Looking Type Bump

I started getting a red itchy welt looking type bump that was kindof puffy/raised on the very top of my butt. It slowly faded into a white flat mark on my butt and it doesnt itch anymore. I started getting it after i went indoor tanning. It was almost as if i got a really bad itchy sunburn on my butt and when I itched it, it would turn into a welt. But it eventually faded away but now its like a white patch on my butt and it won't tan now?? Can anybody help me? I'm worried it's cancerous :(