What Causes Delayed Period, Sickness And Mood Swings While UPT Is Negative?

I'm 22 days late on my period, I've had heart burn, head aches, a sick feeling like I need to throw up, but I never throw up, back pains, I've been very mood, and I've been feeling sick every time I get hungry. I took a pregnancy test, but it came back negative, but I'm still having signs of pregnancy. Could I be pregnant?