What Causes Brown Spotting During Menstruation?

The last two times my boyfriend and I had intercourse, he has told me that he feels something at the end of my vagina that is round and hard. The way he describes it is as if it is covering the entire backway by my cervix. He says that it feels like the size of a baseball. I also have a regular menstrual period, but this month it was just light brown spotting. Could the two be related?