The last time I had intercourse was April 4, 2011. The last day of my period was April 3, 2011. I haven't had a period yet, but I have taken 4 pregnancy tests over the last two weeks and they have all come back negative. Is it likely I'm pregnant? I'm 26, could it be premenopause?

Possible it is perimenopause, but unlikely. It may just be an off cycle... which is far more likely the case.

Wait another week and see if your period is just late. If still no period, try another pregnancy test, making sure you follow the directions. Still negative, wait until next month and see if your period shows when expected... test again, and/or see your doctor, if need be.