Why Am I Not Having My Period For Six Months?

i havent had a period for 6 weeks i am on the pill and i have had a hpt and a blood test from the docter and came back neg i have had a cyst remove 3 years ago from my overies and have been on 2 different types of pills and i had the bar removed from my arm when i had my cyst remove .
i have had abdominal pain back pain nausea but not vomiting and pain in my breasts for the last week.