Period concern

Ashleiy
My period ended about a week ago. It was a littler shorter than usual. 4 days opposed to 5. On the 4th day I had inter course and it started back up again a little ( which sometimes happens I know) but since it ended when I wipe I have a very light light brown spotting. Hardly anything but I am worried. This happened last month too. I got off birth control about 6 months ago. Just curious does anyone else have this happen ? I talked to my gfs and some said this happened to them and some said it only lasted right after their period. We are ttc and I'm concerned this might affect it. It may just be old blood expelling but I wanted to get other opinions. Also I usually ovulate on cd 16-17 and I'm on cd 12 now if that helps. Any advice is appreciated !!