The toilet bowl in the Master bathroom has a very low water level. It has been getting lower and lower over time. The toilet bowl tank has the correct amount of water in it, so I am not sure as to why when I flush the water level in the actual bowl has been decreasing? Can anyone shed some light on this and is this something I can fix. I am in a fairly new home (4 years old).

The bowl is refilled by the little tube that puts water in the overflow pipe.