call jerry springer.....Hell give you one of them dna test for free.....

On a real note, Some girls will just do that to put you in a trap, their scandlouz like that, you know how it goes, you meet a girl, you break up with her, she still wants you to the point shes stalking you, and the only way she can keep you in her life is by saying "im pregnant" and your the daddy.....seen it happen all too many times with my homies and what not........

but yeah def get that blood test done, thats the only way you can be 100% sure.