morning after pill scare

I had taken the morning after pill after having sex with my boyfriend and as usual, a week later had the bleeding that the pill causes. But then the following week (which was the week of my period), I had a very light period. It wasn't heavy, it wasn't heavy enough for a tampon. It was light spotting red blood but mainly was just brown discharge. What could this be? This week my breasts have become tender and have more discharge than usual, which is usually pms symptoms but I'm not sure. I've also been stressed a lot. Any one have any idea on what it could be?