I took metronidazole for a yeast infection, but washing with water 2 days later my vagina still burns!

It could be your skin is still a little sensitive after the yeast infection, but I would want to make sure you’re not washing IN your vagina. That can cause another yeast or bacterial infection. I would give things a couple more days and if they don’t improve (or if things worsen) you could see your doctor for reevaluation.