Negative pregnancy test, Extreme pregnancy symptoms

I'm 19 and sexually active with only one partner. Me and my boyfriend never use protection, he just pulls out, but I've heard that you can get pregnant from pre-ejaculation. I took a home pregnancy test, and it turned out to be negative, but I'm wondering if there's a possibility I could still be pregnant. I've been experiencing symptoms for close to a week now.. I'm tired, moody, constantly queasy and nauseous (I have almost no desire to eat anything.. The thought of eating makes me sick to my stomache), heartburn, lightheadedness and dizziness almost to the point of blacking out, some cramps, headaches, and occassional hot flashes. I haven't missed a period yet, but I should start sometime this week. I'm wondering if I could be pregnant and the test is negative because maybe it's too soon to tell, or maybe it's a tubal pregnancy, etc. Please help!

If you are doubting the results of store-bought pregnancy tests vist a doctor and tell them that you want a quantitative HCG done.