have you checked the pressure in the tank ? You need to use a tire gauge and check the pressure on the tank , there is a valve to do this just the same as on your car tires . The pressure in the tank when the pump is off and empty or no water discharging should be the same as the kick in pressure on your pressure switch, about 30psi. If a tire gauge shows no pressure you tank is shot, if it shows low pressure use an air pump to boost it up to equal the pressure switch kick in pressure .The pressure switch is usual labeled showing settings , you want to match the low number
2 psi below pump on is the proper precharge pressure.
GENTLY push on the tank as if you were trying to tip it over if it feel like it is full of water your tank is shot.
There are a number of things that can cause low pressure, for trouble shooting, in no particular order.
-is pressure tank full of water and pump short cycling – ruptured bladder, this will cause fluctuating pressure.
-check whole house filter cartridge, replace cartridge if needed.
-do you have a water softener? place softener in by-pass to see if pressure increases.
-check faucet aerators
-well pump weak(test by running ohm test on start and run, pump windings)
-well pick-up screen plugged-pull pump to clean