Im not having my period and not PG...?

I have amost all of the signs of PG, but im not, and i have been tested fo everything like stds, cysts, all kinds of everything and i still havent had a period my hubby and i are trying, adn just getting shot down. How come I am getting the short end of the stick and i havent had my period since dec 29 06 and its now march 9 07!happy new year to me huh? please help, any incite is greatly appreciated, thanks.