Hi, Pregnancy is a consideration but I am more concerned regarding the possibility of what is called an ectopic pregnancy, where the implantation occurs outside the uterus and even can occur behind the uterus. This is one possibility that could cause the back pain. This would need evaluated immediately, in an emergency room as this can be life-threatening. Vaginal tears also can be a cause of this, particularly after intercourse. This can cause back pain and doesn t present usually with any discharge. Muscle strain can also be a possibility after intercourse. I would state that I think you do need evaluated in an Emergency Department, if this is an early ectopic pregnancy, it is a life-threatening event and needs diagnosed immediately. Please consider this! Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. David Girardi, Internal Medicine Specialist