There could be many reasons you see low water pressure in your bathroom. For example, the shower pressure could be especially low due to clogged pipes or nozzles on your showerhead. But, first, make sure the water valve is open fully to ensure the proper flow of water. If the valve is open and functioning, clean out the showerhead and check for improvements. The next step would be to check the pipe for blockages and leaks. Leaks along the shower arm or even the water pipe leading to your shower can cause lowered water pressure.  Defective or incorrectly installed water pressure regulators can also cause low water pressure. You may want to call a plumber if this is the cause of low pressure in your shower.