Why does my vagina get sore and swollen after sex?

Swollen Vagina: It is common for the labia to swell during intercourse, as the state of arousal rises. A sore vagina, however, indicates that there is excess internal trauma or friction that might respond to personal lubricants. Sometimes, it is a simple matter of physics - your partner's size may be the cause, and if personal lubricants don't help, you might explore more comfortable positions/techniques for you.