The answer to 'why is my pipe overflowing' is that the pipe is clogged or blocked, causing water to back up and overflow. Common causes include hair, soap scum, food debris, or other objects getting stuck in the pipe, preventing proper drainage. Symptoms include slow draining sinks or tubs, gurgling noises, and water pooling around the drain.
If the overflow is minor, you may be able to resolve it with a plunger or drain snake. However, for more serious clogs or if the overflow continues, it's best to call a professional plumber. They have the right tools and expertise to safely and effectively clear the blockage and prevent future problems.