Question - I owe money in federal taxes and don't know why.

Hey Y'all,

For the first time in 11 years of Active Duty, I owe money in federal taxes (~$1500) and I have no clue why. I have not changed anything in regards to Federal Witholdings and that tab under MyPay doesn't list any incorrect information. Y'all have any ideas how how I might be able to track down what happened and fix it for the future?