M from india.if my last sex with a girl was 14 months ago but if she now has a big belly, that means if she is pregnant baby cannot be mine(since she has not delivered yet) or else cause of her big belly is something else other than pregnancy.right?

That is correct: All human babies are delivered by no later than 9 months after sex, plus or minus 2 weeks. That's the way it has always been, and that's the way it shall always be. The only exception is in vitro fertilization in which a new baby is conceived in the lab, but the embryo is frozen for the future. Some weeks, months, or years later, the embryo can be placed into a woman to start her pregnancy.