is this Decidual Bleeding?

I am concerned about my cycle. I had a mis carriage in July- possiblely the second of two in three months. After i miscarried, my period was clock work for about three months. Then I had three mini periods in six weeks. All three were light bleeding but very dark. In december i had my regular period three days late but normal bleeding and it ended on the usual time. My husband and I were unprotected on the 28th of Dec (my period ended on the 12th). I did not have a period, until Jan 22nd. It lasted two days and was very dark. The third day, there was tissue strands and that was it. Four days later during intercourse a little light pink fluid but no bleeding at all. I had taken three pg tests previous to the wierd bleeding but all were negative. I have been very tired and feel the same kind of ethereal thing I did during my last pregnancy.

My question is, could this be decidual bleeding? Could I be pregnant?
Note: I have had minor endometrosis and cysts previously.