Make sure you have the drain valves in the closed position. Recently, I had the same issue and experienced this newbie (me) mistake. ...forgot to close them after I drained the fresh water supply after a trip. Went to the dealer and it took them 30 seconds to fix!!
I had a similar problem on my 2018 four wind 28z. It was the strainer near the water tank was completely occluded with junk. You can disconnect it clean it out thoroughly, reconnect and should work fine. Good luck. Everything is a learning process!