Please read if you had HSG!

I had an HSG this cycle and now I have started what I believe to be my period. It came very early this cycle and it is not very heavy but it is very dark brown. I also have been passing what looks to be tissue (not clots). This is all new to me and have not experienced this during any of my previous cycles. Could it be just from the HSG cleaning me out? Any advice or experiences are welcome!