Hi Pain Lady,
If you are using this as a screen name, it must be how you identify yourself and you must be in a lot of pain, I truly hope you can find relief soon.
But to answer your question. 75 pounds is way to low for someone your height, your BMI would be around 16 which would make you underweight and very very frail. Even at 85lbs you are borderline underweight. I think you might have the wrong idea about what "normal weight" is. I suspect you regularly talk to your doctors about the pain but have not talked about the weight. My advice is please talk to your physician about your specific weight issue, they know you and your condition better. Also learn more about BMI http://www.healthcentral.com/diet-exercise/index-1688-143.html which is the relation to height vs weight.
Wishing you a pain free future
Move Your Body, Move Your Life
Kenn Kihiu
http://www.dancexfitness.com