A little help here

Ok I need help here... 

I'm almost a month late. Nothing new. I've had PCOS since I was 12. But I've been regular since November, and I went to the dr Thursday and had a pap. She said I don't have PCOS anymore, which would explain why I've been regular. I woke up yesterday with a massive headache and ended up puking. I've taken 6 tests in the last month and all are negative, including the one I took last night. Wth?? She prescribed me a fertility medicine that I filled today, but still? She wants me to take a blood pregnancy test too just to be sure, but if I was pregnant, wouldn't pretty much any test show positive this late?