the doctor should have said smth, even if is ectopic pregnancy. or it could be ur 8 weeks is miscalculated as ur ovulation could be much later. u can also request for a hcg blood test to see if the number is high enuf. the number should double every 2 days to have a viable pregnancy. or worst case scenario is u detected the pregnancy early but u only get to scan now at 8 weeks but it's a biochemical pregnancy so u dun see anything. soon u will have menstrual blood flowing.