Have you tried reversing the left and right speaker outputs to see if the problem is with your equipment or your ears? No offense intended! If the center changes to the opposite side, you likely have an equipment issue.
Are the left and right sides of your room acoustically the same as far as symmetry, dampening, reflective surfaces, furniture etc.
Is this a new problem? Have you changed anything recently?
Have you tried another source?
Does it happen with all recordings?
Do you have a decibel meter that you can test the output levels with while playing pink noise to see if both channels read equally?
Have you tried unplugging and re-plugging the cartridge connections and all other connections making sure they are snug? Have you reversed the connections to see if the center moves to the opposite side.
You could try reversing the left and right connections of each component one at a time and try to isolate the problem.
Too vague of a question to pinpoint, but these are my suggestions.