First, did you have a gain? You may be able to avoid taxation on the gain on the property, at least the portion due to the time you lived in it fro 2011 to 2012, because of your orders with a PCS change to Italy; we would need more information to give you a full reading. However, any gain that occurred during the period you rented out the house (2012 to 2016) may be taxable because during that time period it was an investment property, and different rules apply to investors. You may also owe gain as ordinary income on the portion of any depreciation allowed while the property was held out for rental.
Your situation is a bit complicated, and very dependent on the specific dates, amounts, and tax filings in the years since you purchased it. I would urge you to consult a tax professional, such as an Enrolled Agent (EA), to sort out the pieces. There are several EAs besides myself who post here and would be happy to help.