I have had the same problem as well since around freshman year, I used to have pretty big boobs, but I began exercising a lot, and they've slimed down, taking off your bra at night would help, because they will have a chance of not rubbing each other, also it would be cooler, but I also use baby powder, and taking a shower right after you workout. Also don't use scented soap, or lotion, or spray around that area. It's a sensitive area, if you are at all allergic to fragrance ( like me ) scented things will agitate it.