What Causes Abdominal Pain And Brown Spotting With No Menstrual Period?

hi doc, please i had an abortion on the first week of january and was told after 42 days my period will come. but it did not come as they told me so i phoned the health care centre to inform them about it and i was invited to do some ultrasound and i was told my womb is clear but as at now i have not have my period but each month basically every 14th of each months i experience a sevare abdominal pains and i see a light brown traces just for a minutes, and if i want to go to toilet it really hurt. pls what is the cause.

am in my mid thirties, height is 5.4ft