hi there are many reasons for bad breath from mouth. As you mentioned your bad breath may be from tongue you can use tooth brush to clean your tongue it may reduce your problem. also check your water intake. if you are working in ac office then water intake will drastically drop whic causes dehydration of mouth and may lead to bad breath.
Next Steps
regular water intake, tongue cleaning gently along with brushing and flossing
Health Tips
instead of listerine better use plain water or salt water