My gf have two reguler period of 5days full after sex nd now she miss period she is pragnent ? or if not thn what is reason for miss period ?

Do you mean...: You had sex a couple months ago, she has since had 2 normal periods, and is now late for her 3rd? If this is what you mean, and you have not had sex since then, she's not pregnant, or at least it's very unlikely. Women miss periods all the time . There are many reasons for a missed period - stress, polycystic ovarian syndrome, malnutrition - are a few possibilities.