Bad breath can be due to stomach problems, while within the mouth the cause can be bacteria. If this problem appears while you're wearing braces or aligners, the first piece of advice is to have a clean below the gumline around the teeth (similar to removing tartar, but aimed at reducing the bacteria that have built up under the gums). The patient may be advised to use an anti-inflammatory mouthwash for a while, but unfortunately a mouthwash or any other product applied in the mouth is usually not enough on its own without a professional clean. This procedure is carried out at the dental practice and can be recommended by the orthodontist or the general dentist. Of course, the patient will also be given hygiene instructions to stop the problem coming back. There may be other causes of bad breath too, so see your orthodontist or general dentist if this happens to you.
This answer is for general information. Your own case needs an examination by an orthodontist.