The first thing you should do is get a pressure gauge. You may be confusing low flow with low pressure. At this point, you are guessing about how much pressure you have. Check both sides of the PRV. It could be the PRV is shot or in need of adjustment. Since you have a PRV, there should be an expansion tank between the PRV and water heater. The pressure in the expansion tank should be the same as the PRV is set to. Next, what kind of pipes are in your home? If they are galvanized steel, they very well could be corroded nearly shut and needing replacement. Are there valves in the lines that could be partly closed? These are some of the things you need to do/check.