How can i treat bad breath after my filling fell out?

Start with the: Basics until u see a dentist. I'm not one but a filling coming out should not result in bad breath unless there is food caught in the filling space or infection which i imagine would be painful. Scrape your tongues make sure no food is in there use mouthwash, just do it, drink a lot of water and get in to see a doc that can fix it and give u better info.

2 problems: Seems like your are describing 2 problems, the worst of which is the filling fell out. See a dentist & he can ( together with you ) get you on track to solve these problems.

Replace filling: You are trapping food debris and bacteria in the area where your filling used to be. Replace it.