Are you using a filter? That happened to me once and I tracked it down to the blue Camco in-line filter which was on its last legs. It had settled and was clogged, and let very little water through. Pressure was good at first, but quickly reduced to a trickle. Removing it from the equation solved the problem.
Geoff & Jill
& Sierra, the little white monster
2013 Ford F-150 XTR SC Ecoboost
2015 Jayco Jay Flight 24FBS