I Am Sexually Active. My Last Period Was November 15th.

I am sexually active. My last period was November 15th. As of today (January 27th), I've missed 2 periods. I've taken 3 pregnancy tests, all have come back negative. My November 15th period was also very late (almost a month). For the majority of these period-less months I've had a brown discharge (I understand that this is all old oxidized blood - but why do I have so much of it?!) Also about a month ago (2 weeks after my first missed period) I had one day of heavy dark red bleeding, so I put a tampon in and assumed it was my period but I woke up the next morning with no bleeding whatsoever. I haven't had any nausea, sore breasts, etc, however I've been unusually tired and fatigued for the past few months, even before I missed my period, as well as light headed. Is there any other explanation for all of this? I know my body well and I know something is wrong. Not sure if this helps, but I'm prone to ovarian and bartholin cysts and I'm also anemic.