Lite Spotting 2 weeks after my period...what is it?

I had my period about 2 weeks ago. I recently have changed my diet and been working out. I started spotting yesterday morning. What could it be. I had sex yesterday morning and on my husbands condom I noticed brownish coloring from my discharge. It isn't much spotting, but I still am worried. I don't think I am pregnant. My breasts had been hurting for about 3 weeks which was weird...but they don't hurt anymore. Could it be just a change in diet and exercise? My periods generally are about 3-4 days with large blood clots. I have never spotted before. I had a miscarriage about 5 months ago. I am nervous...Just a big worry-wart