The answer to 'why is my P-trap frozen' is that a P-trap can freeze when the water inside it freezes due to extremely cold temperatures. This is a common issue during the winter months, especially in unheated or poorly insulated areas of the home. When the water in the P-trap freezes, it can cause a blockage and prevent water from draining properly.
Some common signs that your P-trap is frozen include slow or no drainage, gurgling sounds, or water backing up in the sink or shower. To resolve this issue, you'll need to thaw the frozen P-trap. This can often be done by applying heat, such as with a heat lamp or space heater, to the area around the trap. However, if the freeze is severe or you're unable to safely thaw the trap, it's best to call a professional plumber who can properly address the problem.