What would cause missed period and two positive pregnancy tests other than pregnancy? i should have been 19 weeks, but i found out i'm not even prego

Chemical pregnancy: You may have had a chemical pregnancy or a blighted ovum, where the embryo never develops. The HCG that makes the pregnancy test positive comes from the growing placenta. If there is no embryo, the placenta stops growing. Usually you bleed at that point. I can't explain why it's been 19 weeks, but if the test were positive, you were, in a sense, pregnant.