how do i know if i'm pregnant?

if you have sex on your period, like a day before it ends, and he doesn't cum in you but he has precum, and you aren't using protection, can you get pregnant? because i'm only 15 and about a week ago i had unprotected sex and i can't get a pregnancy test because i don't want my parents to know. i feel like i have more flab on my stomach than i usually do but i could just be paranoid or something. i don't know what to do, but i'm not ready to have a child. he isn't really the kind of person who would step up to the father role either. so is there any possible way i can be pregnant now off of precum? is there a way to tell if i'm pregnant without going to the doctor, getting a pregnancy test, or waiting a month until i get my period again? please help. thanks!