I have a rash on my legs and stomach...?

and back anywhere my shirt or pants touch my roommate change the washing powder and i know that has to be the reason i went and bought some other kind i always use and started washing my outfits in that how long will it take for my skin to stop itching it has got bad it started the past week i could not figure out what was wrong. Is there anything i can do to stop my body from itching and heal faster???|||If you take some benedryl your symptoms could clean up within a day or 2