Try a smaller amount of water at first. Even just one cup. When you hit the 5-7 minute mark, you might feel some cramping. I take really deep breaths and blow them out and that helps me hold past that point with no trouble until 15 minutes. You might have to work up to more than 5 minutes. The temperature of the water as well as how fast you let it drain in can both affect how long you can hold it before cramping. I do better with fairly warm water and let it in slowly (over several minutes).