Let us help you fix this problem in 4 simple steps.
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.