31 years old, no pertinent medical history, mother of 5 year old

My hubby and I are trying to conceive and after taking 2 negetive pregnancy tests, my period began Feb. 11.  They only last 5 day MAX - never fails.  Well, around day 5 period was  coming to a close (brownish blood) and following day began light pink/red light to medium and HAS NOT stopped yet.  Some days I notice a small clot or 2.  Bleeding is heavier after orgasm - no intercourse.  No abdominal paid, no medications....any ideas?  Starting to get worried......