I'm having twins as well. Im 14 weeks 2 days right now. I found out at 5 weeks 3 days because I was having horrible back pain & uterine/groin cramps to where it hurt to walk. Also, my blood levels were 27,000 at just 5 weeks ... WAAAYYYY higher than it should have been with a singleton.
Im currently pregnant with twins. We found out after the third ultrasound so a big shock for us. I had a slight feeling that we could have twins because my belly was rounder, more peeeing, veryyyyyyyyy tired and no appetite. The way before we found out I dreamed about twins and watched a lot of twins pregnancy on YouTube.