vaginal itching after sex ?

okay so i went to the gyno about a week ago and she checked me for everything & never called me to tell me bad news so i'm guessing everything's fine. but i've been with my boyfriend for 4 years and i know he doesn't have any std's but every time we have sex the day after my vagina is soooo itchy and red i can't figure out what it is. there's no weird discharge or smell either. we don't use condoms or anything