I agree maybe you are testing too early. Did you test in the morning? Your HCG levels are most concentrated then? When are your periods due? I would wait 2-3 days and test again. If you think that you may not be pregnant then go see your doctor if you have abdominal pain which is not 'normal' e.g. menstruation-associated, ovulation-associated.
You could be pregnant and just testing to early. You should wait a week and test again. Other things that could cause those symptoms are upcoming period, ovulation, ovarian cysts(mine made me feel pregnant), also hormonal imbalances(which can be caused by tons of things). If it continues you should definitely see a doctor.