What Causes Swelling Around Vagina After Intercourse?

Hi, I am a 15 year old girl around 145lbs and 5feet 3inches. I lost my virginity October of last year (unprotected he pulled out before ejaculating) then had sex agian with a different guy in January (protected and he pulled out as well before ejaculating) then yesterday i had sex with another different guy (protected) but he had a thicker penis than the other 2. now the area around my vaginna is red and kind of swollen and sensitive to touch. also ive noticed it to be very dry with lack of my normal discharge. can you please help? and tell me whats wrong and what i need to do?