I'm having some issues with the hot water in my shower. When I turn the faucet to hot, the pipes under my kitchen sink start to bang. The pipes continue to bang until I turn the shower faucet to warm (actually lukewarm. It makes for an uncomfortable shower). The water pressure is also low, though not intolerable. If I turn the bathroom sink or kitchen sink faucet on, the problem is remedied. The hot water in my kitchen and bathroom sinks are fine all the time. Any thoughts?

Other information you may need to help:

The house was built in 1946. I've lived there for almost 3 years. This problem just started a few months ago. I have copper pipes and a gas hot water heater. I'm on city water.