I suffer with these as well and I've asked so many doctors and they all have no idea. For me, they come on after I've been standing my feet for an hour or so cooking in my kitchen, and I'll sit down and it comes. Ugh so painful, seem to start at the left, then maybe to the right or a little lower in the center. They seem to rise up like a flexing muscle, reminds me of labor because it hurts so bad and I have to bear down, then have slow breathing after that.I hate them and I know I've had them for maybe 20 years. Wish I had an answer. I already take Flexeril and potassium as some have suggested. The only doctor that offered me any hope at all is he said it's probably a gas bubble in your intestine and it moves around. I guess it does make sense but I can't take them.