Spotting?

Kaley
Sooo.. I've no idea what's going,on and I would like some help, any help. I was supposed to get my period on the 11th of this month, but never did. For about, I wanna say, two weeks before that, my low back ached and my nipples were sore to the touch. About three or four days ago, my boobs, not just nipples, because VERY sore/sensitive. Like a sore muscle type of feeling. I've also had slight cramps on and off the entire time. This morning, I woke up to some deep/dark red almost brown blood, but didn't know it was there until I went to the restroom. Fast forward 10 or so hours and it's still there, but no where close to bleeding like a period. Not even enough to fill a tampon nor pad. Any ideas why this might be? TTC #1 so any input will be greatly appreciated. (: