What Causes Brown Spotting In Mid Of Menstruation?

Hi I am a 36 year old healthy female. My periods are always on time and all my paps have been normal. I finished my period about 2 weeks ago and have a brown staining when i wipe. I have had this in between my periods for the last couple of months. It lasts a few days and then its clear. Should i be worried. I dont seem to have any other symptoms?