Water pressure in shower

Assuming that the shower is the standard mixer tap type........

If the pressure at the tap section is good then you should try unscrewing the shower hose at the tap end to see if you have pressure there.

The shower heads always suffer from a build up of limescale so it may just be it needs cleaning. If the shower head is new check for a rubber grommet which are sometimes fitted.....

I have to take off the shower mixer valve to clear out limescale about once a year. Shower head needs cleaning or replacing about every six months. You may find filter nozzles on your taps need unscrewing and cleaning from time to time too. Most hardware shops and Chinese supermarkets have these.