Suggest Cure For Heat Rash

Its been nearly a year and a half since i developed what i believe to be Miliaria or heat rash. Its become almost disabling for me, as it occurs when i do anything that causes me to sweat. I can't even mow the lawn anymore without having to stop and run water over my skin to relieve the pain. And another thing I've noticed is my skin becomes very oily when i do anything physical. It even happens when i get nervous. I was wondering if you can help me find a way to prevent and/or cure this problem so i can continue with my life like any normal teenager should