please don't read and run!! tummy pains/cramps at 9 weeks. advice please!!

They were on and off every now and then. It felt like a heavy dull ache and it came in waves of pain. Like period pain. I'm now 9 weeks pregnant and still having the same pain but more often. I have them on and off all day everyday. And I can't work out why. It can't be a miscarriage as 1. I've had them since day one and 2. I've seen a heartbeat already at 7 weeks. Any idea as to what else it could be? My doctor said not to worry and that's fine but I'm just curious. 

I wouldnt say it's mega painful but I also wouldn't say they're dull. They do hurt. And they come in waves. And then it eases off. I've been checked for a water infection and it's not that so what could it be!? I know they say stretching but it doesn't feel like a A stretching pain!? Help please!  X