What Causes Red Bumps On Shoulders And Chest?

i have red bumps on my back shoulders and chest. They come and go but mostly the are there. One doc thought they were chicken pox. Then went to another doc and he gave me Prethizone. It cleared up in one week. But after a week they came back. i live in FL so the heat could be factor. Im not on anything new with meds, detergent etc. What could this be and what should I do??? please help i have seen so many docs about this and everyone gives me meds for someting different.