Gaining weight

I have Celiac disease (extreme gluten intolerance) and ever since I switched my diet I've just been losing weight even past my normal bmi. I can't seem to keep the weight on w/o gluten but obviously gluten messes me up really bad. To illustrate 3 week ago I was 123lbs as of today I am 112lbs. If anybody knows how I can possible get back to my healthy weight (128-140lb) I would be very very very appreciative. This extreme weight loss is making me really self conscious, I can feel my hip bones and my rib cages and I am just really unhappy with how I look now. :(