I just noticed having a blackish maybe dark brown discharge yesterday. When I went to go to the bathroom I saw blood. Does this mean I just started my period? And what is the discharge?

In order to tackle that question, I would need to know how old you are, whether you are or not on the pill and if this happened when you thought you were supposed to get your period or in between them

I am 15 and a virgin but I take the pill to lighten my periods...

I don't think there's anything to worry about dani (by the way, I'm a Dani too). Sometimes you forget to take your daily pill or you have stomach problems that mess up with how the pill is absorbed and those kind of things happen. Some medicines also have the same effect.
If it doesn't stop after a few days, go to the doctor and he will probably run some tests but there's most like nothing wrong with you.