Good morning K.,
I'm going through the same thing actually. I'm about 22 weeks with my second child. My first pregnancy was litterally amazing. I had a few aches and pains here and there, but honestly nothing to complain about. Same goes for my second pregnancy. I was told by my OB that I would have ligament pains (these twinges, and crampy pains you're speaking of). She said that if I wanted peace of mind, to of course call her office anytime. She also said that as long as there was no spotting then I should be all set, otherwise to call her office.
I hope this helps you. I think bottom line is, if you feel you should call your OB for peace of mind, then go for it =) That's why they are there. They want you to be stress free, healthy, and more importantly, they want to see a healthy baby as much as you do. In the meantime, try not to worry. (I know it's easier said than done, because believe me, I'm a worry-wart). Just take one day at a time and of course you always have us mommies on Mamasource too ;)