Eating Disorder?????? Doctor's Appointment

Hi I am a 16 year old girl, weigh about 90 pounds and am about 5 feet 3 inches. I haven't had my period for a year and a half, so I have been seeing a doctor in my community for the past sixth months. At the last appointment, I hadn't gained any weight. I have been eating so much! Oh and I am a runner, so that doesn't help.
My doctor said that since I can't gain weight I need to see a doctor in sports medicine, who will help me with trying to gain weight. But, I don't really want to gain weight. Since I am runner weight just makes my life more complicated. So, I am going to a children's hospital in my area to see this doctor. Next week I have a DEXA scan, which I guess is suppose to see if my bones are healthy. Will the doctor say I have to stop running until I get my period? I am scared that she will take away the one thing that I love to do!
It is obvious that my community doctor thinks I have an eating disorder but I gained a pound and a half since the last visit three weeks ago. This is just so frusterating!!
On top of all this I am getting oral gum surgery in the next two weeks, meaning all I will be able to eat for a week is liquids, so I will definitely lose weight. This is an awful situation. What should I do? Is the DEXA scan scary? Do I have an eating disorder? I am just confused and annoyed by the whole situation right now!

[T11GAR]

Hi

The DEXA scan will NOT be at all scary....you just have to lie still.  It is important that if any damage has been done to your bones that it is picked up and treated, as if you were to develop osteoporosis later in life it would be very painful and really affect your quality of life.  
I guess deep down you know whether or not you have an eating disorder...you have to be very honest and think about whether you think you are fat and if you are truly trying to gain weight and how you will feel about this if you do? Or are you trying to gain weight short term to get everyone off your back and then plan to drop weight again?
If that is the case you maybe do need to speak to someone about eating disorders.  
If however you are genuinely trying to gain weight and feel ok about the thought of gaining weight then you probably just need to speak to a dietician who can help you look at the best ways to do this.

Good luck. X