What Causes Recurrent Abortions And Abnormal Bleeding?

Hi i am 31 and have had about 5 incomplete abortions, i went to see a gynecologist for the 3rd one because of abnormal bleeding. Instead of D&C i had a pill inserted into me (4 pills on dosage). After that i went in for an ultrasound scan and it indicated that i was clean. However i still experienced this 5 months later. My husband and i want to have a child but this happens everytime i think im pregnant. How can i stop these abortions and get prgnant?