Your social security benefit is based on your 35 highest earning years in your work history. You can download your work history from your social security online account or the social security administration may mail you a statement once a year.
You will have to look at your history. If your current earnings are less than they were 5 years ago, but are still more than you earned when you were 25 or 30 years old, then your current earnings will still be increasing your benefit (although less than before) because they will knock out one of the old low earning years and replace it.
