What Causes Constipation And Spotting A Week After Normal Period?

For the last week I haven't been having as many BM as usual and yesterday I started spotting and it went from light brown to dark brown and has gotten a little heavier, but it isn't too heavy. I've changed to a healthier diet the last month and I have been exercising a lot more. I guess there could be a chance that I'm pregnant, but that's unlikely because I never had sex with my bf, he just fingered me and there might have been some pre-fluid on his fingers, but he didn't ejaculate so I don't think it's possible. Also I've gotten my normal period since this occurred and it ended a week before the spotting happened.