Sometimes women just miss a period all together. I have had it happen a couple times, and every time I would wonder if I were pregnant, get negative tests, and continue wondering. Then come the following month I get my period right on schedule. My doctor informed me that it is normal and happens to 80% of women about once every year or two.
But the pp is right, you would be showing a positive by now on a test. But see your doctor and get blood work done, just to be sure. Hope all goes well!
By now if you were pregnant you would be coming up positive on a pregnancy test. Best thing to do is contact your doctor and request an physical exam and maybe a blood test to rule out pregnancy. The exam may be able to help you find out why you haven't been getting your period.