I had prolonged, massive vomiting for hours. im having leg cramps so im guessing its electrolytes. what can i do for this?

Drink: some Gatorade/ Powerade or Pedialyte, or natural coconut water. Those have the most consistent concentration of potassium (and sodium/ chloride) that you need to rehydrate. You can also go for some grapefruits ,oranges, bananas and other fruits with potassium. Keep drinking water, 1 L every hour while you have diarrhea and vomiting. Cramps don't always mean electrolytes, they could mean water