Can we back up one second? I have to give you a great big hug. 15 pounds is NOT huge. It may feel like it when you look in the mirror, but no way are you huge if you are 15 pounds over the weight you'd like to be!
I'm sorry your family's not supportive here, because I know that would be a lot of help. But I think it's so helpful that you know your sister has celiac disease and that it may be what's bothering you as well.
Were you able to look at some of the celiac disease links I gave you, and are you trying a celiac inspired diet yet? If so, how is it going?