It's pretty hard to get a false positive on a pregnancy test compared to a false negative, and sperm can live a long time in the woman's reproductive tract. Women often write in who doubt their prenatal test results, always ones who did not test with both men. I assume you didn't test with the other guy?
If the guy you want to be the father refused to test, wait until the baby comes, and do a DNA test of the kind that is certified by the courts to determine paternity, and do it with both guys. The courts will not take prenatal tests as evidence for establishing paternity, and you will need a court-approved DNA test. If the guy from November continues to refuse, see a lawyer. You are not obliged to tell the attorney that you got a prenatal test with the first guy that said he is the dad, since it can't be used as evidence anyway. And besides, you aren't even convinced it is accurate.