why do I spot two weeks after my period and is it something to be concerned about?

I am on cd 13 and noticed a bit of blood in my cm. Why is this? I had it last month too. I never spot other than when a/f is coming and it is only the day before she comes, but this is has happened now to times and I do not understand it. It is only there when I wipe and I have no cramping or anything just a stringy discharge with a small bit of blood.

Thank you