Am I pregnant? Right? what do you think?

Hello! I would really really like to get some help and advice. I would like to know if I might be pregnant or no. I had unprotected sex on feb 25. My last period was 8-12 feb so my ovulation day should've been on feb 22. Since the egg is ''alive'' only 12-24 i should be ok, but ovulation day might not always be on the day it's supposed to and I am being so paranoid.. My period should start tomorrow but there are no signs that it's starting(usually I can understand it). All my friends have told me that the possibility is so small because I am certant that he didn't come inside me but sperm is microscopic right? And you will never know.I'm not feeling sick and my eating habits are normal but I am feeling a little pain in my lower stomach area sometimes but it might also be upcoming period pain. My friends are telling me that I'm just thinking over and that I'm thinking the pregnancy sympoms for myself and that my period might just be late because of stress. What do you think?