Finally, after years wondering what kind of skin disease that I have, I finally found the answer. Keratosis pilaris so what it calls.
I've gone to many doctor also dermatology, but none of them give me a satisfaction answer for my problem cause they always gave me a different answer for my disease. Some of them said that it was because I was wear a wrong kind of cloth/fabric, that it didn't soak the sweat well so it cause that kind of rash. They gave me some medicine, but it still not cure....