Absolutely freaking the hell out

So I’ve been with my boyfriend for 3 months this coming june 7th. About two weeks before we started dating, I’d slept with two other people. Since then, I’ve had two periods. They were regular, normal, and just like every other period I’ve had. I just found out I am a week late (I’m not the best at period tracking) and my boyfriend had told me he’d done all the testing, and was unable to have kids. But here I am, three months in, one missed period, haven’t slept with anyone else, and I’m pregnant. There’s no way the kid could be one of the other guys right? I’ve had two periods since my last partner. Is it just a miracle? Boyfriend was lying? I just NEED to know it wasn’t my last partner. That line is DARK for just a week late.

EDIT: I am already a mother of one, and my stomach has not grown any. Especially for being my second child, I am sure I would have at least SOME tummy at near three months pregnant