I'm almost 3 days late on my period...could i be pregnant?

Ok, so on January 22nd, me and my boyfriend had unprotected sex and he came inside me...well the next day I had a lot of eggwhite discharge, and according to my period app, I was in the middle of my 'fertile' week...its now almost february 7th, I was supposed to start on the 5th. My periods are never late either :/ ...I'm not having any symptoms of pregnancy or my period, but for the past week had horrible headaches, been very tired, and i've been a garbage disposal, eating anything and everything I can get my hands on. Is it a waste of $ to buy and test now?? What are the odds I could actually be pregnant? I didn't have any implantion bleeding or anything..any advice?