What To Do After Missing Periods And Getting Negative Pregnancy Tests?

Hello, i just wanted to know whom to consult in regards to checking pregnancy, whether i am pregnant or not? I had my period last month on 03/02/11 7 today is 18/03/11 still i did not have my periods & i did two home pregnancy test but both were negative so don't know what to do? Should i wait for few more days for period to come or i should consult GP or GYN?