Am I pregnant?

[CaseyKachel]

I'm 22, and have always had a very regular period. I had light spotting about 5 days before my period was due, then it turned dark brown/black. My period was very light and lasted only 2 days (normally it's 4-5 days long), with cramping.. I have never spotted before my period before and I normally don't cramp. I use the Nuvaring for birth control, and put it back in on the day I was supposed to. My breasts (mainly the nipples) have been very tender, and that's not normally something that happens from my birth control. I've taken 2 at home pregnancy tests, first one didn't work, and the second one said negative.