People say is not good to douch even less after a yeast infection but can i douch just with plain water after using 1 day monistat and when can i sex?

Don't douche. : People say it's not good to douche for a reason. When you flush the vaginal vault with water, commercial products etc, you upset the normal balance of bacteria. This can set you up for a yeast infection or bacterial overgrowth like BV (bacterial vaginosis). If you're confident you have a yeast infection (vaginal itching, white discharge, no fever etc) treat the yeast, but skip the douche