Way to go! 50 pounds is incredible!
I also get heat rash in several places, which has gotten worse since I've lost weight. It's not every day, thankfully, but it is still a problem. I now wear a good sports bra (LOVE the one from Lane Bryant) and a pair of Spanx to hold myself together, lol, and after my shower I apply a baby diaper ointment to the rash. Just the cheap Wal-Mart brand. It helps sooo much. Good luck!!