Based upon the IRS website:
For the American opportunity tax credit, an eligible student is a student who: (1) is enrolled in a program leading toward a degree, certificate or other recognized post-secondary educational credential; (2) has not completed the first four years of post-secondary education as of the beginning of the taxable year; (3) for at least one academic period is carrying at least ½ of the normal full-time work load for the course of study the student is pursuing; and (4) has not been convicted of a felony drug offense.
From: https://www.irs.gov/newsroom/american-opportunity-tax-credit-questions-and-answers
The American Opportunity Credit is for the first certification or degree that you are pursuing. In this case, it appears that you are no longer eligible for this credit, based upon when you first began the program.
