Depends what you mean by "symptoms". I felt implantation at 6DPO but no other symptoms. Most symptoms are first caused by HCG, and then the increase of estrogen and progesterone. If you don't have enough HCG in your system to pop a positive, then it doesn't make sense for you to have enough HCG in your system to cause symptoms.
I "felt" pregnant on the 2 cycles that we actively tried, and not at all on the one that we NTNP and actually got pregnant, so I know that your mind can really play tricks on you.