The sex in dreams is interpreted as an omen of your intimate life either mental or physical one. The dream could be a reflection of someone in your life that is very close to you. Having intercourse with your partner means that you love and dear him/her very much. Sometimes the sex with some person doesnt show the actual and sexual affection to him or her, but it simply shows that you would like to be with this person more. If the sex is unpleasant during your dream, you are unhappy about your life or relationships with particular person. Sometimes teenagers have these kind of dreams because of the sexual maturity that they getting into.
Read more about dreaming of Sex in other dream meanings interpretations.