My daughter had the same problem. She was given a hydrogen breath test and was diagnosed as severely lactose intolerant. The hydrogen that was building up cramped her terribly and made weird sounds in her gut. This is going to sound weird, but also...with lactose intolerance, when you pass gas it smells REALLY horrid, like sulfur. Can you tell if it's any worse after milk or milk products? If so, try eliminating all dairy for a week and see if you feel better.