Lynn's answer always is good advice. There are several 'first time buyer' mortgage programs out there. Many do use the 3 year rule-- not since the date of purchase but since the date you last had an ownership interest in REAL ESTATE.
In PA , the one that is probably the most often referred to currently is the Pennsylvania Housing Finance Agency option. Check out the details at this website: http://www.phfa.org
Hope that helps.
Your Cumberland Valley Real Estate Professional