I second and third the posts about conditioner which could be clogging your pores. My hair is now about down to the top of my shoulder blades in the back and after I rinse out conditioner I always pull it to the side and cleanse my upper back with my liquid soap (neutrogena) and maybe a little exfoliating too if I have a breakout.
While I do not condone sun worshipping, I do find that brief sun exposure clears up breakouts!
In general, I'd keep hair off your neck and back when exercising, shower promptly after your workout, and use astringents in the a.m. and p.m. I even use hydrogen peroxide as it doesn't overdry my skin.