I am sorry but this must be a typo. 600-900 mg of oxycodone a day for a girl your size? No way, thats impossible for multiple reasons. First being, you would die from that dose. Second being, the amount of money and resources to maintain that habit is incredible. Unless you live next door to the factory that produces the pills and are able to sneak in every night and take tons of them I dont see this being possible.
My advice for the withdrawals though, your already at day 9 and the worst is already over. Your still gonna feel funky depending on how long and how much you were using. Human brain and body cannot adapt that fast to such a drastic change in your chemistry. Just hang in there and do things that you enjoy doing other than using. Eat snacks, sweets and other pleasure foods. Sleep a lot. Talk to people about how your feeling and ask for advice. Take long walks around the area. Try to be happy, I know its hard, I am trying to quit for the 15th time right now.