Twin parents

So I might have figured out when the first day of my last period was. Which was the 18th of august. I honeslty didnt know 'cause my af was super unpredictable. I got my first strong positive on september 18. At the time I didn't know I was only 3 weeks along.

I work in a clinic and the doctor was in that day. I got an u/s on the 19th of September and we saw nothing yet. Technically I was only 1 week pregnant. But counting from my last af I was 3 weeks along. How early did you find out you were pregnant and it ended up being multiples?

Curious cause I had a dream I was having twins.

Symptoms, small nausea on sept 17 and got my positive on the 18.

Bloat and gas.

Small headaches and cramping.

I haven't had major symptoms yet.

What was yours? And how early did they confirm it was multiples?