Had my baby in 8/9/14, on 8/22 i had unprotected sex. about a week ago i started having low back cramps and brownish discharge what could that mean?

Visit doctor: It could be many things. It could be your uterus cramping back down to normal. You could have an infection. I suggest you visit your doctor for an examination and culture to see if you have an infection. Also I suggest that you not have intercourse for at least 4 more weeks. Your body is healing and it should be allowed to heal without interruption.