What is this rash near my bum?!

Okay this is pretty embarrassing so bear with me. I'm a 15 year old girl, and I have had this weird rash on my upper thighs and at the lower part of my bum cheeks. It doesn't itch, it's just a stinging, burning feeling. I looked at it in the mirror and it's red all around the area that hurts. I have eczema on my hands and elbow creases. I don't think this rash on my legs & bum is eczema because it's not itchy, scabbed, or dry like my usual winter eczema. I haven't put any cream or lotion on it lately except I just put some of my Aveeno Eczema Therapy moisturizing cream on it to help the pain. What is this rash and how do I get rid of it?