31 or 34?🤔🤔 help me understand 😭

So .. here’s a backstory.. I went in to the OB when I THOUGHT I was 8 weeks pregnant.. well when they did the ultrasound the first appointment, she was measuring 5 weeks and like 3 days.. so doctor thought that she stopped growing and that I was going to miscarry.. well I’m SUPPOSED to be 31 weeks and 1 day today.. right? My doctor and ultrasound tech both think she’s measuring 3 weeks ahead, and he keeps saying she’s a “large baby for her age” anyways.. I’m experiencing what I think are contractions.. I’m saying “THINK” because before getting pregnant I don’t ever remember getting menstrual cramps before or during a period. I’d get severe migraines. So I basically don’t even know how a cramp in the stomach area feels.

Anyways.. I’ve been getting them alllll night last night and the night before, to where I’m basically shaking. And last appointment her head was already down and my OB moved her.

Idk I’m just worrying.. what if I’m actually 34 weeks instead of 31? Is that possible ?? What do you ladies think?