Late period, pregnancy symptoms, negative test

My period is now 4 days late, which I know isn't a lot of time, but I've also been feeling quite sick, peeing a lot more and my nipples feel sore when touched. I bought a Clearblue digital test last night but it said I'm not pregnant. Is there still a chance I am or is it unlikely? Could my mind/body be tricking me into feeling symptoms just because I so desperately want to be pregnant?