My gynae told me that my ultrasound shows i have a 9 weeks sac but my foetus is only 7 weeks old.i also have bleeding now.How is this possible?

Because pregnancy starts during your 'last' period. Pregnancy begins even before conception. So that means your body was already preparing for the baby (which is what it does after your monthly cycle) before the sperm and egg were joined. Hence...you are nine weeks pregnant...but your fetus is only 7 weeks along because conception only happened 7 weeks ago...but your body began preparing nine weeks ago. I found that weird too when I found out I was 7 weeks pregnant when I had sex only 5 weeks prior. Hope that helps.