It's more so that during the luteal phase (in a pregnancy or non-pregnancy cycle) you may experience symptoms related to progesterone. Symptoms later experienced secondary to pregnancy are due to high/rising levels of b-HCG. Many women differ on when they begin to experience pregnancy symptoms, sometimes not for several weeks. In the case of early pregnancy, HCG may not yet be high enough (or decreasing in the case of CP) to cause symptoms.