E.L.
When I was pregnant with my twins, I was starting to feel pretty miserable at around 5 weeks. All of the symptoms I had with my first two singletons were extremely exaggerated with my twin pregnancy. I was also showing so early, that by the time it was confirmed by ultrasound, I pretty much already knew I was having twins. Everybody is different, though. You won't know until you get an ultrasound, so try not to stress too much, and get yourself to the doc! :-)