What Causes A Prolonged Menstrual Period?

Doctor, I really dont understand my condition now. I have a problem of irregular periods from time i attained puberty. Now, last month i got my menses on 8th of august and in september i got it on 17th of the month. I started taking Lynoral from 21st as advised by my doctor, twice a day... My periods are generally long, as in i have heavy bleeding till 4-5 days and after that darkish fluids from 5th to 9th or 10th day. This time, I had unprotected touching of genitals with my husband on 23rd thats the 7th day,(in the morning bleeding was there but in the evening when the bleeding wasnt there), And still i got dark fluid on 8th day...Could you please clarify whats going on. Also i m still taking lynoral, 0.05 mg twice a day.