There's nothing more important than having a house with no water. Especially since it seems to stop flowing while you're using it, and that is usually after hours like 7:30 PM on Friday night with a holiday on Monday. LOL
It sounds as if you have a leak at higher than 39 psi. That could be a broken fitting or loose hose clamp on PE pipe. Shut off the water on the house side of the pressure tank when the pressure is up to 50 as the pump shuts off and watch the pressure gauge.
If the pressure falls, the leak in on the house side. If it holds, open the valve and watch, if it falls it's a leak back to the pump or foot valve in the well; usually in the drop pipe or the check valve in/on the submersible pump outlet or the foot valve for a jet pump system.