If you are having unprotected sex while on your period, is it possible to become pregnant?

Yes.

How is it possible if your not ovulating?

The sperm can stay in you for a long time, they can wait there until you're off your period and until you ovulate again. They're strong little buggers

The sperm can stay in you for a long time, they can wait there until you're off your period and until you ovulate again. They're strong little buggers
I'm sorry, but this is incorrect.
At most, sperm can live up to 5 days in the right conditions. The right conditions include fertile cervical fluid which is called "eggwhite" in layman's terms. Sperm cannot live in menstrual blood for long and will most likely be flushed out.

However, because it can live for up to five days, you are able to get pregnant around your period. Sometimes ovulation could take place as few as 8 days after your period ends. Its also possible that you're spotting during ovulation or for other issues and it isn't an actual period. Basically, you should use protection at all times because without charting basal body temps, cervical fluid, and cervix position with possible OPK's you can't know exactly when you're ovulating... it can happen at any time during each cycle.