Heat rash for 3 weeks

I developed what I think is a heat rash about 3 weeks ago after an all day canoe trip in the hot sun. It's mainly all over my arms, shoulders, and a little on my sides. At first I thought it looked like lots of tiny acne with several white heads, but it seems really odd to have that on my forearms.

I've tried to keep cool and stay out of the sun. Also, been using a salicylic acid wash and acne cream with no improvement. I know believe I have heat rash. However, everything I've read on-line says it should just go away in a few days and to use anti-itch creams, but it doesn't itch at all, it just looks terrible.

Any suggestions?