If the doc does the ultrasound I think you may see a heartbeat, I didnt get my first ultrasound until 12 weeks and i saw the heartbeat, we didnt listen for it yet because it still may be too early. If you have the ultrasound it will make you feel a whole lot better I think. If you were pregnant with twins I think you gain weight faster sooner. but can't be sure until you see both of them in there. Also the sex isn't normally told until I think I was told 18-22 weeks so they can be sure. I am hoping to get the sex of my baby on my next visit but will only be 16 weeks. I have heard that in the beginning they all look like they have boy parts until the baby matures enough for it to grow inward for a girl. or out for a boy. I hope this helped a bit.
Good luck at your appointment