It could be a UTI, prostatitis, irritation from
alcohol and dehydration from the
alcohol and flying, or a host of other things, including an STI if you suspect your wife of going outside the marriage, but honestly, the only way you'll know is to see your doctor, get an exam and do some testing.
If you take the metronidazole, and it doesn't work (which it likely won't), you could end up screwing up your testing.