What Causes A Delayed Period With Negative Pregnancy Test?

Hi my name is isabella I'm 14 and I'm 5'3 in. I had sex with my boyfriend and we didn't use a condom.. I'm 36 days late on my period and I have stressed out and have no symptoms of pregnancy whatsoever.. I've also taken the at home pregnancy urine test twice and they came out negative... I was wondering if there is a possibility for me to get pregnant? Or is it just due to stress my period is coming late?