What Causes Foamy Vaginal Discharge After Having Sexual Intercourse?

My fiancee are trying to get pregnant, we had sex One time he "let himself go" inside of me, we had sex again about 20 minutes later he did the same again. I went to the restroom after word to clean myself up and I noticed that there was thin foamy like substance coming from my vagina, is that normal? If not what could be the possibilities?