It needs to be your primary residence for at least 2 of the last 5 years. If you didn't move in until March 2013, then that is when it became your primary residence. If you sell before it is your primary residence for two years, then you will owe taxes on the capital gains. That would be the sale price, minus land+build costs, minus sale expenses (including commissions). Details can be found here:
http://www.irs.gov/pub/irs-pdf/p523.pdf
Agreed, and don't forget to include "improvements" in your cost basis. If you moved in during March 2013, but continued to have expenses for fixtures, etc along the way after you moved in, all those costs get added to your basis, which will reduce your capital gain if you don't meet the 2 of 5 year exclusion. You can't count maintenance cost, but improvements.
Also read page 14, "Reduced Maximum Exclusion" of IRS pub 523. If you are moving due to health, new employment (50 miles), or unforeseen circumstances, you may still be able to avoid the full capital gain tax bill.
With that said, if there's any way you can wait until you meet the exclusion, that's the best option because any other option could require much calculating and paperwork.