Old blood from birth control during sex

Patient: I was on Implanon for the past 4 years and never got my period. I had it removed in November and got my tubes tied in December. I have had 2 normal periods since then. Evry time I have sex I have a brown, smelly blood present. Is this the old blood from the years I didnt get a period? If so, how long does it typically last? Any info would be greatly appreciated. Thanks!