Assuming that you are not getting water to all of your faucets - including the shower - you might try:
1) checking the water line from the FW tank to the pump. It is possible that it may be clogged with debris. You can check it by removing it from the pump and if you have a compressor, use it on low presssure to blow the line out.
2) the diaphragm in the pump may be stuck or damaged. There are usually 3 set screws that can be removed, exposing the diaphragm. If it is damaged, you can often find a replacement at an RV supplier. If it is stuck, clogged or dirty, remove it and wash it in warm, soapy water.
3) It is possible that if your display is telling you that the FW tank is full, it may be giving you a false reading and your tank is empty.
If you aren't getting any water just in the shower, it may be due to a clogged mesh in the shower head.
Hope these suggestions help.
And "Welcome to the Forum"
2008 Cougar 5th Wheel 27RKS
2005 2500 GMC Duramax