Raider
Not sure if you have a manual, but you can get one here.
https://www.monacocoach.com/rv-owners-manuals
Look at page 293 for items listed below.
Several things could be happening. First, Check at the Wet Bay area (where you hook up water) that the City water/Fresh water Fill Valve for filling the Fresh water tank is completely turned off. If left open or partially open, pressure will be lost going into the tank. Is there any water in the Fresh water tank? Do you get pressure when you turn on the water pump? If you get pressure when the water pump is on but none when you have it off, it is possible that the check valve is malfunctioning.