My master bathroom shower head has very low flow rate. I've change several heads and still the flow is low. I took off the shower handle and the back plate to see if I could adjust the hot and cold water that is coming into the handle. However, there seems to be no set screw that controls the hot or cold water on either side. I've seen videos online where there should be screws on either side to control temp/flow rate for the cold and hot water coming into the shower and you can adjust it using a screwdriver. But, it seems mine is not setup like that. So what are my options to increase flow rate? Should change the cartridge then to see if that helps? By the way home was built in 2005.