What Causes Brownisg Discharge After Menstruation?

My last period ended about a week ago. It seemed normal. I did have sex on the third day of my period. Now four days after my period I have a very dark brown cervical mucus. I have never seen this before, and I always check this stuff. It only appears when I wipe after peeing. There is no smell, but its kind of thick. I do not have any pain. Should I be concerned? This is day three and its not getting any lighter.