I think if you took a morning after pill, it is normal to have an abnormal cycle afterward. However, your cycle was abnormal before you took it. If you weren't having a period, you weren't ovulating so it would be unusual that you all of a sudden ovulated the one time you had sex. I would say it is very doubtful that you are pregnant. Remember, you hit your body with a hefty dose of hormones with the morning after pill.
I personally would see your doctor to discuss why you hadn't had a period in years. that is very unusual at your age. good luck
Hello,
If you are apprehensive regarding the status of your pregnancy you can get it checked. Most home pregnancy tests that check urine beta-HCG are sensitive to 20-25 mIU/ml of HCG. The test can be positive anywhere from about 2-3 days prior to a missed menses to 4-5 days after, but usually it should be done 7-10 days past your missed period.
Otherwise you can get a serum HCG also done which is more specific than urine pregnancy test.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.