What should you do if you had an abortion awhile ago and can't get over it?

Therapy. Seek counseling from a therapist, psychologist, clergy member, or psychiatrist. Antidepressant medications are also sometimes used.
Therapy. I'm sorry you're having trouble coping. You can always see a therapist, or even just talk to a trusted friend. There are also non-judgmental hotlines available - such as Connect & Breathe (http://www.connectandbreathe.org)
Above all, know that you are not alone - abortion is very common. It is a difficult decision for many women, but it is nothing to be ashamed of.