I suffered with this when I was younger and I have some scarring which I hate. I got some topical cream from the doctors and going on the Pill sorted it out (you don't have that option if you're male lol). It came back briefly when I came off the Pill to get pregnant.
It's most likely your hormones, the pill will definately help you out. You could also get one of those long loofah's and give your back an extra scrub while in the shower every morning, that should help out too by keeping the pores unclogged.
Keep your back as clean as possible and try to wear cotton tops as much as possible, synthetic materials make you sweat more.When the weather is nice try to sit out in the sun with your back exposed,the sun will help clear the spots up. I always get a spotty back in the winter and it clears completely in the summer just by me doing this.