An 18-year-old patient complains of liquid foul-smelling discharge from her vagina, discomfort during sexual life. Her menstrual cycle is irregular. Examination of the external genitalia detects hyperemia and edema of the vulva. Examination in the mirrors shows that the vaginal mucosa is hyperemic, the cervix is clean, the discharge is profuse and foamy. What is the most likely diagnosis in this case?