Just because you are drinking plenty of water does not mean that you are "getting" enough. That is to say that if you train and sweat a lot, you will have low levels of electrolytes, which will make it difficult for you to regain and hold the correct amount of water. Many people suggest bananas because of their potassium content. The fact is that there are lots of other ways to get potassium. Kiwi actually has a high concentration of potassium by weight and coconut water is also a good source. Potassium is just a useful electrolyte. Also, if you are low-carbing, it makes it difficult to take water into the muscle because this is done along with glycogen; something which is depleted with a low carb diet. Fruit carbs (fructose sugar in general) is useless for reloading glycogen into muscle, so stick with starches. You may try a gatorade and half a roll of sweet tarts a half hour before training and see if that helps to remedy the cramping. Stretching a cramp can be bad news, btw (stretching a "dry" muscle or a cold muscle is generally a bad idea). I hope that this helps.