Hopefully you're using something similar to this as your regulator?
NOT THIS! This is called a regulator, pictured below, but is actually a restrictor, it restricts the flow regardless of pressures rather regulate the pressure. They are also famous for sticking & nearly shutting off the flow.
Best option to anyone using this type is to toss it & use a "regulator" if you're not doing so already.
For better shower head function replace those POS factory shower heads with an Oxygenics head, it mixes air with the stream to feel like more pressure while using less water.