Single-dose metronidazole is about 90% effective for trichomonas, so there is a 1 in 10 risk your treatment failed. Higher doses (2-3 days treatment) sometimes is necessary.
However, I can't say whether this might be causing your discharge. Metronidazole and other antibiotics can trigger yeast infections, but the main symptom of yeast is itchy irritation, not discharge. Up to 20% of women with trich also have gonorrhea or chlamydia, and every woman with trich needs to be tested for those infections. If not tested, or if your discharge persists, return to your health care provider for further evaluation.
Good luck-- HHH, MD
Thank you for your advice. I was tested for gonorrhea, chlamydia, and HIV last week. I am not received the result of the test. I think I will return to my doctor.