Need help !

Really confused. My husband and I had unprotected sex the time I was ovulating. These whole two weeks since then I've had cramping on and off which I don't usually have unless I'm starting my period. My period was supposed to come yesterday but it hasn't. I went out and bought a Early result first response test but it said negative. I have a strong feeling I'm pregnant. I've had symptoms like cramping, peeing more, dizzy spell which came out of the blue today. Could my hcg level be to low to show or should I be testing positive at 4 weeks if I was really pregnant. Has this ever happened to someone with the same test I used? I'm pretty bummed 😞