Water Pressure

Hope this isn't too dumb of a question! :@

We don't get good water pressure when hooked up to water in our Class A Winnebago. I have even taken off the outside water filters and just run a direct hose to our hookup and still not much pressure. Our water pump has more than from the water system, but I guess that's to be expected.

I know that there is a check valve thingy in the rig connection so water doesn't syphon out. Could that be acting up and need changing? If so, how do you get to it?

Any other suggestions as to why the water pressure is so low? Sometimes there isn't enough to get through the shower head. It was replaced about a year ago, so hope that isn't it.

Thanks for any suggestions.