Voting laws changed in 2014. All U.S. citizens outside the United States who want to vote by absentee ballot must complete a new Federal Postcard Application (FPCA) every year if they wish to vote from abroad. You will no longer automatically receive ballots based on a previous absentee ballot request.
http://www.fvap.gov/citizen-voter, Federal Voting Assistance Program (FVAP). FVAP is the official U.S. government website for overseas absentee voting information.