Your period might not be that regular. And ovulation can really happen at any time, even during your period. Sometimes, if the guy cums outside, but very, very near the opening of the vagina, the sperm can find their way inside. And you could get pregnant if his penis was inside your vagina, but he pulled out before cumming. Even though this is the least likely time for you to get pregnant, it does happen.
Women can ovulate at any time, even during their period.
And menstrual blood can transmit HIV, so you should definitely practice safe sex during your period. Or you can wait and see if your period comes on time and get a pregnancy test if it doesn't. Tender and swollen breasts. Having to go to the bathroom a lot. Changes in mood and appetite.