Trich is hard to diagnose in men; none of the commercially available tests works very well. But if 2 separate partners have had trich, especially if it seems likely you infected them, you probably have it.
Despite common recommendations for single-dose metronidazole, which works well in women, no research has ever shown whether it is effective in men, and stories of treatment failure (like yours) are common. You should ask your provider for more prolonged treatment with metronidazole, e.g. 500 mg twice daily for 5 days. Or get treated with tinidazole (trade name Tindamax), a newer drug well studied in men, effective in a single dose of 2 grams. (But much more expensive than metronidazole.)
HHH, MD
Have YOU been diagnosed? If not, that's the place to start.
I have never had trich but I have taken metro for bacterial vaginosis. It was prescribed 2xday for 7 day. I'm wondering if your getting the right amount. One dose doesn't seem like it would work.