More important is that on which day of your cycle you had unprotected sexual intercourse.
If it's prior to midcycle you can take emergency contraception within 72 hrs of unprotected sexual intercourse like i-pill.
Vaginal irritation may be due to rash or infection which needs proper treatment.
Next Steps
Clinical evaluation for vaginal irritation.
Watch for other symptoms like fever burning & itching
Health Tips
Drink plenty of water and other fluids.
Eat healthy full mixed diet.
Maintain perineal hygiene.