Is Missed Period Sign Of Implantation Phase?

Using pull out method for 1 1/2 months. Period due on 6/2/11, 2 weeks late. last tiem using pull out method was 6/12/11. Took test at doc's office,neg. told to wait until end of month to retest, don't start birth control. menstrual like cramps a few days ago and today, no bleeding yet. Could I be in the implantation phase?