A pregnancy test will generally only come back positive if there is HCG in Urine, and there is only HCG in urine when you are pregnant. There is nothing else that could cause HCG to be in your urine.
However it does seem a bit early to already be having pregnancy symptoms, and normally pregnancy tests are not accurate until about 4-5days before your expected period. I would take another test or go see a dr and get a blood test.