What Causes Brown Discharge After Menses?

I have been having dark brown discharge. My periods are normal, not heavy, on time more or less. but when it ends in the few days brown discharge comes and less for another week or so, i feel a little bid discomfort, but no sharp pain or anything like that. I am 43 years old. my last period started June 1, less for about a week, and then i started to have this brown discharge again about June 10-th. Today is June 15-Th, my breasts are tender like before the period... I am freaking out.. what is going on with me??? I scheduled appt with my dr, but it is only next week, and i am so worry...............Please help!