Many women may mistakenly think they have an allergic reaction to sex.
A small number of women do develop an allergy to proteins in semen. But more often a burning swollen, red vagina is an allergic reaction to using condoms and lubricants.
Women sometimes assume that it's the latex in the condom that's irritating them, but really it's more likely that it's the spermicide in the condom that's causing a reaction.
There are condoms without spermicide, but obviously they are less effective at preventing pregnancy.
How, then, can you get relief? Apply a cold compress right down in the middle of the affected area, and you can also take a benadryl - an allergy and anti-itch medicine - to relieve some of the swelling and irritation.
It's also important to rule out other causes of vaginal irritation, such as an STD like herpes. Also, menopause is associated with more vaginal dryness.
If the irritation continues, see you doctor to find a suitable remedy.