It is incredibly unlikely that you’ll be pregnant, as you’re not fertile (there’s no egg to be fertilised) on your period. However, sperm can survive in the body for about a week, and if you have short or irregular periods it’s theoretically possible that you could ovulate in the few days and that egg could be fertilised. This is incredibly unlikely, especially if you have regular 28-day cycles, but you may wish to take emergency contraception just in case.
It also sounds like you had unprotected sex with a partner you haven’t been exclusive with for 6 months or so, so an STD test would be a good idea. Scarleteen is a great website you can check out for more sexual health information, including what to expect and how often to get tested.
What are your contraception plans going forward? I know you said you didn’t want to be lectured, and I don’t want to lecture you, but having a plan in place in the future is a good idea!