I'm actually concerned the absence of your periods could be something more serious than pregnancy. You should have popped a positive by now. You really need to go to a doctor and find out whats going on.
Have you tried taking a blood pregnancy test? Do you have any type of pregnancy symptoms? I would go to your dr and get a blood test done. Thats what happened to me. I missed my period for 2 months and took 4 home tests and they were all negative so I went to the dr and had a blood test done and that came back positive. My dr said the home tests were negative because my hormone levels were to low to read.