Why do you feel you should be paid more because you feel you are doing more work? You are paid the least amount possible to fill your position during the hiring cycle. Your worth is what the market will pay you.

The fact that someone else is doing more or less with a higher title shouldn't influence your life at all. Jealousy shouldn't tell you when you should look for a job. If you are unhappy leave if you are happy stay. If your happiness is determined by what a random person is paid you will never be happy.