My son had really bad breath when he first come to live with us as a foster child. Right away I started brushing his tongue because it was covered in white. It took a while and it went away. I think some of it might have been from lots of sugar and candy. We don't eat a lot of that and it hasn't come back.
Also watch every day and see if it's worse on certain days. It may be a food issue allergy to something like milk. Could also be reflux.
My Father in Law used to have terrible breath too and once they realized he had diabetes and got it under control it went away.
Mom to 4, soon 5 through another adoption and hopefully more :o)