With the limited information, it sounds like the problem may be the pressure switch not cutting off properly.
If the WellX pressure is about 18 psi when the pump is off and the water pressure drained down, your pump must be set for 20-40 psi cut-on/cut-off, and the tank bladder is O.K. The tank pressure should be two psi below your cut-on.
The pressure relief valve (on the water heater I assume) should not leak until the pressure is 150 psi, so it may have some debris in it. Open it wide open to flush it out, and then close it and see if that solves the leaking.
I would replace the pressure switch. Make sure that all lines and connections from the pressure tank to the switch are cleared of any clogging.