When individuals undergo weight loss, they may undergo ketosis. When you first reach ketosis, the body doesn't really know how to regulate the fats it breaks down. As a result, it makes a lot of waste ketones, which are then released in breath and urine. As time passes, it will become more tuned and the extra ketones will reduce. Until then, make sure to drink plenty of Water to help flush out the waste.
After Weight Loss Surgery, your body is converting your stored fat into the energy that drives your body. Thus you lose weight. But in the process your fat cells are breaking down and being expelled from your body through sweat, urine, stool, and breath. After you transition from weight loss phase into the maintenance phase, this problem should be less noticeable.