What could be causing this red line between my breasts?

Since I was about 16 (I’m 21 now), I’ve had the habit of wearing my bra to bed. Since about 17 or 18, I also wear two camis (tight ones) every day, even at night.

…don’t ask.

Anyways, some time ago, probably well over a year ago, I noticed a red line right in between my breasts. It’s hidden when I have a bra on because it’s directly in the crease that my bra/camis create. I used to go to the tanning bed and each time I went, the area between my breasts would itch so bad that it hurt. That’s one of the many reasons I stopped tanning.

I stopped tanning about a year ago, and the crease is still there. About a month ago, I went to my dermatologist and she said that my bra was “pinching the crap” out of me and to stop sleeping in it. I did what the doctor ordered, but I still sleep in my camis, which she said was fine.

So it’s been a month and the line is still there. It’s very faint in the morning, but after I get out of the shower it gets much darker. It doesn’t hurt or anything, so I figured it might be very dry skin. I’ve been applying lotion in the mornings for a couple of weeks and it doesn’t seem to be helping.

I vaguely recall the line going away during the summer when I spend a lot of time out of my bra and in a bathing suit, but I’m not totally sure. I’m a bit of a hypochondriac, so I naturally assume the worst. However, this isn’t really a symptom of anything I’ve heard of.

I’m trying to comfort myself since the dermatologist said it was my bra, but why hasn’t it gone away? Any thoughts on what could have caused this and/or ideas on how to make it go away would be awesome. :)