What Treatment To Be Taken For Red Itchy Rash Appearing On The Thighs?

hello, on friday i started with a red itchy rash appearing on the inside of my thighs,the skin on my torso under my boobs and on both my underarm areas an a little on my chest, it gets worse when im hot, but i read heat rash should go after a few days and mine is still here 5 days later, i ve tried antihistamine and they don t seem to work, the only relief i did get for a little while was after my last bath yesterday i scrubbed the areas to exfoliate the skin till it was sore, can help me please