Confused?? Late period or paranoia ??

My boyfriend and I are going to be in a six month relationship soon. We started having sex and We did recently. I was supposed to get my period almost three or four days ago. I've been having cramps but no implantation bleeding or any signs at all of pregnancy. I'm scared to tell my parents cause I don't know how they'd react and I'm too scared to buy a test, any ideas on what I should do?? I'm scared and don't know what to do. I'm only 17 and got my whole life ahead of me just need some advice asap.