How does twin pregnancy feels like?

I'm 5 weeks and 4 days pregnant, this is my third pregnancy. I've have not yet have any morning or night sickness. But I'm experiencing a little bit of cramping pain on my back and sides.. And I'm already should and my belly button is starting to poke out. Is that a sign of expecting 2 baby's? Have not yet gone to the doctor but my appointment is this coming Tuesday. Please help