I agree with the other poster. You need to get a pregnancy test. Yes, some women can have a period or light bleeding during pregnancy.
If you're having sex and you're also having irregular periods you might want to think about getting on the pill. It will not only protect you against an unplanned pregnancy but it can regulate your periods. Maybe that's how you can put it to your mom. You want to get your periods regulated so you'll know for sure when to expect them.
Get a pregnancy test first. Before you get to stressed. If you are pregnant stay in touch with the app where you can get plenty of advice. Regardless of the out come you will be fine. Life doesn't always turn out the way you it expect it to. Let me know how u get on.