I have really bad breath/dry mouth?

Lately I have noticed I have digusting breath. I brush reguarly and use mouthwash but it doesn't help. I also have a white coating on my tongue, but it usually comes off when I brush, there's just some plaque buildup on the back of my tongue that I can't reach. I don't think its thrush because it doesn't look like any of the pictures of thrush and I have allergies/sinus drainage issues. How can I cure my bad breath? Its so embaring?