Emergency sonogram

My first appointment was scheduled March 11th but they checked my HCG and they are more than doubling in a 24hr period. They said it is good indicator it could be twins. Not only that but my progesterone is measuring at a level of someone in their second trimester. So they scheduled me in this Wednesday to see if they can spot twins. I'll be a bit over 5 weeks. The only thing they can think is, twins, I'm further along than what they previously thought, or I have a VERY active baby.