You can insist on an u/s if that would put your mind at ease (especially if you are a private patient) . My obst. did an "in house" one on his little machine so I could see the baby at about 8 or 9 weeks, and I'm sure you can hear the heartbeat at 8 weeks but I could be wrong.

My first preg. I had similar sharp pains which were the uterus expanding etc. But only sporadically.Mention it again to your doctor if you are worried or get a second opinion if possible. You are allowed to be as worried as you want, and ask as many questions as you want. You could always go to a public hospital and say you are worried, they often do an ultrasound to confirm things...but maybe not these days... I'm sure it's fine, but you keep seeking the reassurance you need! Good luck.