Possible pregnancy!?

So my boyfriend and I have had unprotected sex at least three times now. I'm fully aware that's not smart, but he lasts very long and when he knows he's about to cum he takes it out and he rubs the rest out. I was wondering if you could get pregnant from precum? My dad's fiancée has me nervous because she told my grandmother I was pregnant when in reality I just gained weight over the past few months. 
BTW: We rarely have sex because my mom never leaves us alone 
Please no one leave comments about under age sex. I'm fully aware we're suppose to use condoms. I'm fully aware that I have my whole life to have kids.