Went for 2nd ultrasound at 8 weeks this time was able to detect fetal pole yolk sac and gestational sac but still no heartbeat not sure why ?

Dating : If you saw a fetal pole and yolk sac, that's a good sign. You have an intrauterine pregnancy. You aren't 8 weeks, because cardiac activity initiates between 5 1/2 weeks and 6 1/2 weeks, so likely you are much earlier than you calculated based on last menstrual period. Hopefully your doctor scheduled a follow up us to detect fetal heartbeat? If not, would recommend, to make sure no miscarriage.