What could be the cause of vaginal discharge, lower back pain, cramping in lower abdomen, difficulty passing urine?

Vaginal Discharge/pa: You probabely pelvic inflammatory disease and you need to consult your doctor, need exam, blood and urine test and if indicated pelvic ultrasound/or cat scan to confirm the diagnosis and proper therapy with antibiotics.

Infection: An infection in the bladder or female reproductive area can cause all your symptoms, this can be a serious infection that requires immediate medical attention, so i would recommend immediate evaluation, better to be safe. Until you know what it is from a professional please avoid intimate contact with others.