Irregular...need some advice!!

Ok, so here is my problem...I was on birth control for a year until me and my husband decided that it is time to start a family. I have been off birth control for 8 months now. And have not gotten pregnant! Very frustrating! My periods before birth control were never on time BUT always regular periods. up until 2 months ago. I got my last period on June 13 and have not had it since. I recently started working out because a friend told me that working out could regulate me, and help in the process of getting pregnant. I worked out for 7 days and felt a cramping in my stomache went to the bathroom, and it was the start of what I thought was a regular period. but as the day went on I realized, It was far from anything I have ever had. I do wear tampons, so when I removed it.....there was hardly anything on the tampon except VERY VERY DARK BROWN almost black looking blood on it! I figured...well I missed my period in July so maybe it is just old blood, and my regular period will start in a day or 2. But it has been the same color and just spotting. I am confused and dont know if I should call the doctor, or if this is regular?? Can someone please help!