What do you think about my situation?

Okay hi. I lost my virginity on January 31 and before that month my periods were always on time. They were always on the 17 or sometimes the 18 but never any later. But after I had sex the first time I didn't have my period in February or March and in April I had an extremely light one(very in common for me) then in may it was oddly a little heavy and lasted 11 days (also very odd) and I didn't get it this month. So before you ask I have taken a pregnancy test the other month but it was negative. And something else confusing me is my dads go is pregnant and she still gets her period. So maybe I am? Idk. That's why I'm asking you. (and something else I didn't explain very well is that me and him had sex more than once over the months. We didn't use any condoms. But please give me your honest opinions)