My shower's water pressure is gradually decreasing. In addition, my cold water knob needs only a minuscule turn in order for my shower to be icy cold. I can't get a comfortable temperature anymore.

I have copper pipes, and fairly old handles. What can a homeowner do without calling in a plumber?

A water pressure quick fix is easy. Take a 1 quart plastic bag and pour 1 pint of white vinegar into it. Place a rubber band around the top and slip it over your shower head securing it with the rubber band. Get as much of the shower head submerged in the vinegar and leave it at least overnight. The vinegar breaks down the calcium buildup in the head and pressure is restored.

Or better yet remove the head to see if there is any change. The bag trick is fine but doesn't explain the touchy nature of the knob. I suspect we will eventually find debris in the mixing cartridge but for now remove the head to see if the problem goes away. If it does go get you bag of vinegar.

The stem needs to be taken out, inspected, washer replaced and stem reinstalled...