FIrst, make sure that the shutoff to the house is fully open. Then, if you have a PRV, it may have failed. Then, take a look where the water comes into the house and try to determine what kind of pipe it is, and what size it is. Then, get back with your observations. A bad prv can show that, but you may or may not have one. Galvanized piping eventually rusts and can choke the volume off prior to rusting through, so if there's any of that, that may be the issue...all it takes is a small section to do that.