Dark Color Period And Abdominal Pain

Hi,

i was a virgin till I met my fiance. Its been about 1.5 months since we have been living together. We have had sex on and off before, but now we are quite regular. The first couple of days since we started were painful, but I expected that. Now I have seen two changes in the past 10 days:
1. My periods seem to be on time and the blood flow is normal. The color of the endometrial tissue used to be normal red. Now, this is the first time, I noticed it was much darker. Kind of black in color.
2. The second change I felt was during the passage of urine. I am experiencing pain in the lower abdomen, kind of in my bladder. Also, I am able to hold for a much shorter time than I was used to.

Does anyone know if its normal? Has anyone else experienced it?