Thank you for your question.
First of all, let me start off by saying that you are definitely not alone in your situation; many people have gone through similar experiences with contraceptive issues, both younger and older.
That being said, it is understandable that you are stressed out by your situation, and being uncertain about something like this can definitely be very confusing. First, a simple way to reassure yourself is to buy a home pregnancy test and test yourself at home: this is a simple urine test that you can do 7 days after a missed period, and that you can buy at any pharmacy without a prescription simply by asking your pharmacist.
I must add that the likelihood you are pregnant is very low, given that you had your usual period after using the after-morning pill. There have been very rare instances of young people with vaginas discovering they are pregnant despite continuing to have their periods, but these cases are very uncommon and usually produce less bleeding than usual as well.
Also, missing a period for a few days because of stress, be it emotional or physical, is quite commonly seen.
In this sort of situation, I would still recommend to seek the advice of a trusted medical expert, perhaps your family doctor, or someone at a CLSC; you can always request a female doctor if you feel more comfortable with that.
Meeting with a doctor, having them do a blood pregnancy test (more specific and sensitive than a urine test) and check-up to ensure there are no complications with your menstrual cycle or otherwise, and talking about this as well as any other contraceptive questions you may have can clear up some of the confusion and stress that you have been experiencing since you slept with your boyfriend, as well as leave you more informed for next time. If you have regular sexual intercourse, you might also want to raise the issue of regular oral contraceptives with your doctor, as well as consider Pap test, cervical swabs, and blood tests to rule out sexually transmitted infections.
It may also prove helpful to talk to your boyfriend so that you and him are on the same page in terms of sex, contraceptives, etc. Communication is key, especially when engaging in sexual relations with a partner, and you need to let him know that this has been worrying you and that perhaps next time it may prove fruitful to take more precautions when having sex, for example, using a condom or adequate and regular birth control. It is always better safe than sorry!
I hope this answers your question. Thanks for writing, and good luck.
Catherine, For AlterHeros