How come everytime ii have sexual intercourse my vagina swells up and burns, why does it do this?

Vaginal pain: If you are using condoms, you may be allergic to latex or the spermicidal lubricant -- if you are not using condoms, this falls under the category of dyspareunia and is best evaluated by your gynecologist.

Friction: I definitely agree with possible allergy to condoms. It could also be related to just the physical act of sex and the friction of the vaginal mucosa that makes you feel dry. This can also lead to the feeling that your vagina is swollen. Another factor could actually be the lubrication you are using. Mineral based lubricants are notorious for making you feel dry. Use water based!