I found out at 12 weeks I was having twins via u/s. But my symptoms kind of tipped me off that it *might* be twins. During ovulation I had very sharp pains in my ovary, I can feel myself ovulate sometimes but this was intense. I called my OB and he said it sounds like I am ovulating strong
. I started showing at 4 weeks, this was my first pg and was very skinny to start with so I didnt think much about it. At 2 weeks pg I starting getting nausea. At 3 weeks (1 week before my missed period) I took a hpt and it was bright positive! My headaches were horrible and I was so tired...My friend had bets that it was twins but I didnt believe her until I saw 2 little babies!!!
If you think you are pg with twins you can always have an u/s. It is better now that way you can find out sooner so you can begin to have things monitored and they also might be able to tell if they are in the same sac and/or placenta. That helps in determining if you will have problems with TTTS and other issues that can arise in a twin pregnancy.
Good luck to you and your bump is adorable!!!
ETA: I wanted to add that the reason I didnt find out until 12 weeks is b/c I didnt want a vaginal u/s so I waited until they could do a belly one.