I am experiencing vaginal irritation, pain with urination (quality: stinging or burning sensation) , frequent urination, missed or late menstrual ...

May have infection.: Reasons for missed / late period include: an anovulatory cycle in which no egg is released, marked v or ^ in weight; eating disorder; Over-exercising (endurance athletics), stress, travel, significant illnesses, oral contraceptives & other meds, Illegal drug use, breast feeding, hormone imbalances and medical problems (i.e., PCOS). Pregnancy is #1 reason. Med eval will help to figure out sx's.

UTI? Yeast? STD?: You may have a urinary tract infection, but other problems like yeast infection or STDs could do it, especially with vaginal irritation. Genital herpes is a possibility. See a doctor ASAP, the sooner the better for effective treatment and for most accurate diagnosis.