Pregnancy

Okay here's my story, before I started dating my boyfriend three months ago I didn't have regular periods. I also have never had sex until I started dating him either. But after I started dating him they came normally for about two of the months. We have had unprotected sex  2-3 times but he pulls out, which I know is not as effective as birth control among other ways. Anyways, I am now a few days late and I took a cheapo pregnancy test and it was negative. Should I be worried or should I take another one that's more expensive? Or could it be that I'm just stressing over it so it's causing my period to be late? I've googled this stuff but no straight up answers lol. Thanks in advance.