When i used to play sports, a general indicator of how hydrated i was usually was whether or not i got a pain in my said. It was usually the right side. You work a physical job and you may not be taking in enough water to compensate for it. Try increasing your water take and see how that goes.

Just fyi, im speaking from my own personal experience. I'm not sure what your pain feels like. Hope you figure out soon what is going on