Let us help you fix this problem in 4 simple steps.
If the pressure is still the same, call the plumber and ask to change the cartridge present in. It regulates the water pressure which only a plumber can fix with the right tools.
Prep. Shut the main water supply to your bathroom. With the help of a tongue plier open the faucets from the wash basin and shower head.
Clean. Open the tip of the faucet and the mesh. Clean all the dirt and gunk. Similarly, open the shower head and clean it.
Clear again. Switch on the main water supply; the water force will clean the pipeline thoroughly.
Last move. Assemble the fittings back. Do not forget to tighten it properly.