The answer to 'why is my toilet constantly running' is that there is likely an issue with the toilet's flapper or fill valve. The flapper is the rubber seal that lifts up when you flush, allowing water to flow from the tank into the bowl. If the flapper is worn, cracked, or not sealing properly, it can cause water to continuously run into the bowl. The fill valve is the mechanism that refills the tank after a flush, and if it is malfunctioning, it can also cause the toilet to run constantly.
Some common symptoms of a running toilet include the sound of water continuously running, the tank taking a long time to refill, or the water level in the tank being higher than normal. To fix a running toilet, you may need to replace the flapper, adjust the fill valve, or clean the valve seat and other components. If the issue persists or you're not comfortable making the repairs yourself, it's best to call a professional plumber to diagnose and resolve the problem.