I would suggest going to the chiropractor. I go regularly. It actually makes your labor shorter and easier
I think anytime you have sharp pains it's good to stop. All the ligaments and supporting tissue are loosening up through pregnancy because of hormonal changes, so it's likely to take more twisting to cause the cracking. But the more you twist and put effort into cracking, the more likely you are to cause a strain or injury or something like that.