What Causes Itching And Pain In The Vagina?

a few days ago i experienced itching in my vagina. The next day i had unprotected sex with my long-term boyfriend. The itching has since gotten worse. There is also redness, my vagina lips are swollen &i have small blisters in my vaginal opening &white milky discharge. We've had unprotected sex before &never had this problem..please help my, i can't sleep because the itching and pain is so severe. I am 21 years old, weigh aprox 70kg, i had a pap-smear about 5months ago &the results said i didn't have any STD/STI. I have had the same sexual partner. He is a med student &tests himself regularly..so i'd say we're both virus-free.