Chronic halitosis since COVID. Got way worse after pulsed Flagyl. Looking for some ideas and guidance

I've been dealing with chronic halitosis since I got COVID back in 2021.

After COVID, I was diagnosed with H. pylori. I did the triple therapy, then spent a long time trying to heal my gut with diet and everything else. The H. pylori was eradicated (I've tested negative since), but I felt like the BB never fully went away. It was probably about 60% better though.

From then until around 2023, I became obsessed with eating healthy because I was convinced my gut was the problem. After about a year of really focusing on it, the BB actually seemed to disappear completely. I would have some halitophobia, but people never reacted.

Later on I tested negative for H. pylori but positive for SIBO. I took antibiotics for it, but I never retested, so I don't know if it actually cleared. I don't think it did because I still have bb. Eventually I started noticing people reacting to my breath again, so I figured something had come back.

Then around 2025, I saw a post on here about a pulsed Flagyl with (metronidazole) with amox. clav regimen that supposedly cured three people. I was desperate, so I tried it.

I regret it more than anything.

Instead of helping, it made my BB about 10x worse. Before, it was at least manageable. Now it's constant and so much more severe. I don't understand what happened, and I keep wondering if I completely messed up my gut microbiome somehow. The bb also becomes 10x worse depending on what I consume.

I'm getting a comprehensive stool test soon to see what bacteria are actually in my gut because I'm trying to get some answers scientifically instead of just guessing in the dark and going based off symptoms.

Has anyone experienced something like this after taking Flagyl or another antibiotic? Is there any explanation for why things would get so much worse instead of better? If you recovered, what ended up helping?

I'm also hoping that if there are any scientists, microbiologists, gastroenterologists, or anyone with a deep understanding of the gut microbiome here, they might have some ideas about what could have happened biologically. Could long-term pulsed Flagyl have shifted my gut bacteria in a way that made the BB worse? I'm not looking for a diagnosis, just trying to understand what mechanisms could explain this.

Some days this has me feeling completely hopeless, but I'm trying not to give up because I know I got rid of it once before. That gives me hope that there's still a way back.

I'd really appreciate hearing from anyone who's been through something similar or has any thoughts on what could be going on.