42 days late on period!!?

My last period was August 27th. I have never missed my period other than when I was on birth control, I had my Mirena taken out May 2012. My birth control is the not the issue because I've had a period every month since the removal till September this year. 42 days seems to long to blame on stress also.. I feel like some pregnancy symptoms come and go, I'm very emotional. I've had 3 negative test, one was a test at the doctor office 3 weeks ago. I done two home test Sunday, both negative. My friend said my levels maybe to low for a test to show up. I don't know, I'm very confused!! A ultrasound cost 1200-1500 which is money I just don't have. If I keep getting BFN, I'm scheduling a blood test!! But does anyone have any similar stories?