I have never heard of anyone that has lost a significant amount of weight from wearing braces. I wore braces and experienced the pain the 1st couple of days after being tightened, but it never lasted enough to effect my overall weight and food consumption.
Your weight has fluctuated within 5 lbs? If so, i wouldn't even stress it. That's nothing and could be due to medication, stress, holiday's, your schedule and when/the times you eat.
If your pains worsen, see a GI doctor.