Your pressure tank sounds waterlogged (lost all of it’s air). You will need to introduce air from the top of the tank. Do this by removing the gauge and draining the tank. This will suck air into the top of the tank. Your pump is turning on and of because of the pressure switch working against water with no air behind it. This is typical for no bladder type tanks. Have you considered a captive type expansion tank?
Respectfully David Walling