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Do you think your boyfriend would be able to take you to the store or pharmacy to get you a pregnancy test, if you are unable to get there on your own? You can also ask a friend to, if you trust them. That way, you won't have to get your mom involved until you truly know for certain what is going on. If you want, you can also go to a doctor or clinic such as Planned Parenthood and they can administer a test there.

I'd try and stay calm until you know for sure whether or not it is a pregnancy, though. Try and take some deep breaths, because things like stress can also alter a person's menstrual cycle.

If you are pregnant, it is wonderful your boyfriend would be supportive! This is something that would take a lot of communication, since you do have options when it comes to pregnancy (keeping the baby, giving the baby up for adoption, or having an abortion) and it is important to pick the best option for you. I'd also try and make an appointment with an OBGYN, since they would be able to monitor throughout your pregnancy.

If you aren't (and in the future in general) I'd start using a backup method. The pull-out method isn't always effective for the reason you described - sometimes it doesn't happen on time. A condom or the birth control pill would add extra protection.

I wish you the best of luck!