How deep is the well? How deep to water? How deep is the pump set, assuming it is a submersible? What is the amp draw, in relationship to the pumps data plate? These are things that need to be looked at, before making a good guess as to what the problem is. But, if i was to give a random guess with the info .you have provided, i would look at a hole in the down pipe, due to corrosion, or a leaky fitting. This is especially common if your driller dug you a dog legged hole, like mine did for 50 homes in my area. But, this is just a guess, and something else to look at. Good Luck!