D.P.
Before I was pregnant with my daughter, I would miss periods, and would have other similar pregnancy symptoms- but all PT were negative. I even went for about two months with no period. My doctor finally did an ultrasound which showed ovarian cysts on one ovary, and a cyst in the fallopian tube. It's possible you have something similar. If you feel something is wrong, then get a second opinion and ask for a pregnancy test. It's not uncommon to miss periods from time to time, but I would get concerned if it went too long.