I always get brown discharge at the end of my period, so maybe it's from that? Otherwise, is he scratching you up there, or maybe rubbing too vigorously or anything? Perhaps it's an infection of some kind. If you don't feel any pain, then that's good, it probably isn't too severe.

Here's a link that I hope you find helpful: http://www.momswhothink.com/womens-health/brown-va...

Since you just became sexually active recently, I think you should make an ob/gyn appointment for a pelvic exam to make sure all is well with your lady parts.

It sounds like you could either have Bacterial Vaginosis or some other infection. I know it's embarrassing, but I would definitely go see your doctor. If you have an infection and it's left untreated, then it could cause great harm to your sexual organs and other issues.