I don't know what the pump cycling off and on could have to do with your pressure getting lower in the home. If the pump is shutting off, the pressure should be the same as before.
If the water is going somewhere, you should determine if it's going into the house or down the well. You can do this by closing the main valve feeding the house. If the cycling stops, you have a leak in the house.
If it's going down the well, you could add a check valve up top, but it is only going to mask a problem that can get worse over time and cause you a lot more problems. So if it's in the well, I suggest pulling the pump and fixing the problem.