Normally the flow restrictor or the shower head becomes blocked with lime or other mineral deposits.

Disassemble and clean the shower head or replace it

Also the diverter can also have a partial blockage like foreign matter like a washer etc.

My tube faucet must be bad. I stuck a rag in the pipe and the water ran well to the shower head. I took the faucet off and its a cheap plactic Standadyne. The flow restrictor is on the end and dosen't look like it come off. I'm going to take my old one to the hardware store and see if a new one won't help.

I feel sorry for home owners who buy a new home today as normally the prime contractor goes for the lowest bid and thus the plumber (if he does this kind of work) has to use the poorest quality and cheapiest possibly products on the market.

I have one contractor here where I do all the repair work after the home is sold and the plumbing installer is long gone.

If you decide to replace your shower body use one T&P controlled for safety