Son had odd rash?

whenever he scratches himself, the skin swells up in to blotches, almost resembling mosquito bites. I made him a dermatologist appt. but its not for 3 weeks. He's only 9, and this has been happening since the summer, whenever a spot itches he scratches, and then it puffs.|||Have you called the nurse at your pediatrician's office? She might save you an expensive derm visit.|||My sister had this as a kid, and still gets it. She only gets it in the sweaty parts of her body, in the arm pit, behind her knees and elbows. It's called a heat rash and it is extremely itchy, gets really red and blotchy. Her kids have a similar rash but the doctor says it's eczema.