I have missed three periods and took pregnancy test which came back negative. I went to the doctor and the did pregnancy test still negative dos any one know what could be up. Thanks in advance.

You need to go to your doctor and hae them verify through ultrasound that you are indeed not pregnant, and then sit down and have them give you an opinion as to why they think your flow has not come. Depending on your age it could be many factors if not pregnancy including but not limited to, PCOS, early menopause, menopause, and endometriosis.

You could still possibly be pregnant... the pregnancy tests are accurate by the time that you take them. And as for teh doctor, there are a few (rare) cases when they screw up. Go again and request multiple tests. By multiple I mean for anything that could be wrong. And another pregnancy test along with that.:)