Go see your doctor. It could be either.
It could be either. It does take a while for the body to re-adjust after being on the pill. However if you had unprotected sex, you could be pregnant. Have you done a home pregnancy test yet or is it too soon?
If you are concerned, you should contact your GYN provider and discuss it with him/her. If you do want to remain sexually active with birth control but not the pill you were taking, there are other alternatives that you can discuss with your provider.