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.
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.