What Causes Soreness On Vagina While Having Sex?

Whenever I increase my sexual activity with my husband, I have one spot on the labial fold near the entrance of my vagina that gets very sore. If we have sex several days in a row, it burns and becomes very painful. I put vitamin E oil on it this time thinking maybe this would help the healing, but now it turned into two round red bumps that look inflamed and it hurts like crazy. They are not blisters and they are not ulcerated. There's no itching and there isn't any noticeable discharge. Any idea what this could be?