What do you mean by "huge"? How many pounds do you feel like you need to lose?
Here is some information that might help. The Mayo Clinic has a section on celiac disease; there are blue links down the left side of the page that will take you to "Treatments and Drugs" and "Lifestyle and Home Remedies" that may help:
The Celiac Disease Foundation has a lot of information about managing celiac disease. Just go here, and you can even download a PDF titled "Quick Start Diet Guide for Celiac Disease":
Since your sister has celiac disease, is she helping you with your diet?