Why don't we ever hear about the first seven Presidents of the United States? 

It's quite simple - The Articles of Confederation didn't work well. The individual states had too much power and nothing could be agreed upon. A new doctrine needed to be written - something we know as the Constitution. 

George Washington was definitely not the first President of the United States. He was the first President of the United States under the Constitution we follow today.

 As Far As the first seven, John Hanson  1781-1782 Elias Boudinot (1783),  Thomas Mifflin(1784),  Richard Henry Lee(1785), Nathan Gorman(1786), Arthur St. Clair(1787), and Cyrus Griffin (1788)  They Are The Presidents Forgotten in History.