Conceive

My guess is super late ovulation. You maybe got pregnant mid October? That seems more likely to me than the idea that you were pregnant that whole time and testing negative for some reason.

From experience your OB will start counting it from I think the first day of your last period. That's how they'll determine your due date. Unless you know your conception date that's what they'll use to determine the due date.

@Taylor if that’s true hypothetically would I only be like 4 weeks pregnant? Lol is it possible to find out that early ?

From my experience, they'll count from period until they get a dating ultrasound, even if you know exactly when you ovulated (this was my case, I had to use fertility drugs so I know when I ovulated). I also work in an ER (clerk) and when pregnant people come in we count based on the dating ultrasound if they have one, and/or send them for a dating ultrasound (we usually see people early in pregnancy when they have bleeding, as they want to make sure its not a miscarriage) As for testing negative, then positive, it sounds like you had late ovulation. When they advertise that you will test positive on the first missed day for pee tests, that's based on a "typical" cycle where you ovulate on day 14 of 28. Not everyone has typical cycles, and even if it seems like you do, you could ovulate early or late.

OB, like said above, will count your last period as start date unless you know when you conceived. The size if the baby in ultrasound may give them an idea if that date is *super* off. You asked above if you can know as early as 4 weeks. Answer is yes. I found out from an at home test at 3 weeks!

I found out around 4 weeks that I was pregnant !

Yes, very possible to find out at 4 weeks pregnant. Could actually find out sooner in most cases I agree with the other ppl that they will default to your last period. BUT also that doesn't make any sense/is an extremely inaccurate way to date pregnancies. It assumes everyone always ovulated on CD 14, which is just not accurate.