I'm breaking out in heat rash-hives-esque bumps all over my body what could it be?

Okay, so a couple months ago right when it was just about summer time (Early June-July) I started breaking out in a heat-rash on my thighs. It itched and itched and then slowly cleared up. Then, it came back and was moving up my stomach and torso and eventually started affecting my sides and now I have an open wound on either side of my hips (almost in symmetry with one another) that haven't healed in about month now. I'm not sure if it's because I keep itching it, but it hasn't made any more healing progress. Just recently the "heat-rash" has spread to my . I have a bruise like bump or two on the shaft of my . What could this be? Could it just be from heat rash and itching? Or could it be something else like an allergic reaction? I have a dermatologist appointment set up for Monday, but I was just curious if anyone has experienced this as well...I've taken Benadryl for the itching but it didn't appear to do anything for it. I've been trying to take cooler showers and drink lots of water but nothing seems to be working...Curious for any thoughts.