I had a new hot water heater put in some time last year my plumbing is old 50 years I think.
Lately lose hot water pressure to shower and faucet ? In bath room only sink is good and cold water is fine what can I do about this issue.

This could be caused by mineral buildup in the heater if it's not flushed on a regular basis. Turn the water off to the valves affected and open them up. Check and clean the inlet ports on the cartridge,
Next turn the hot water back on to flush out the supplies. Reassemble and test. Better flow now?
If you don't flush your heater let me show you how.
For long life and fewer troubles you should keep your heater clear of mineral build-up by FLUSHING NOT DRAINING on a regular schedule. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white or yellow grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. Now flush out your hot water lines on ALL fixtures that are affected . Now pull each aerator and clean the screens. Be sure you put them back together the same way you took them out. Don't forget to flush it out every month. Your heater will thank you for it. Hope this helps and thank you for rating my answer, Tom