What Causes Brown Vaginal Spotting After A Surgical Abortion?

Hi, I had a surgical abortion 2 months and 2 weeks ago. I bled lightly after the procedure for 3 weeks, which continued into spotting for the next couple weeks. My first period after the procedure was heavy as usual, but a few extra light days longer than my usual 4 day menses. After my period finished, I started spotting lightly again, and then almost blackish discharge followed after a few weeks. I never went more than 2 days without having at least a spotting of some sort since. Today, I am still having light brownish discharge mixed with a little light pink blood. What is going on, and why won't I stop bleeding???