Hi,
If you have taken the birth control as instructed, and not been sexually active after the abortion, then chances of pregnancy can be ruled out. In this case, then absent periods could be attributed to the surgical abortion and birth control use.
If you have been sexually active then chances of pregnancy cannot be ruled out.
Visit your treating doctor/gynecologist for a thorough evaluation to look for the cause for your absent periods. Causes like pregnancy, anovulation (no egg release from vary) and damage to basal endometrial lining should be ruled out.
Take care.