How do i tell my mom?

okay so i was supposed to go to a waterpark today but i can't cuz i started my period well i actually started like in january...bu i havent told anyone and i just said my stomach hurts really bad.....which it does...but how do i tell my mom...like i dnt like awkward situtaions, and it's really awkawrd talkingg about stuff with her.. so could u help plz?