White milky discharge with little back pain and stomach cramps feel as though going to have my periods with a weird smell what could it be?

Check STD: If you have been sexually active, and miss your period, do a home urine pregnancy test first. If not pregnant, you should rule out an STD like GC with a pelvic exam and tests for the same, including UTI, by your physician, who may consider a pelvic inflammatory disease as a differential diagnosis for your symptoms. In the meantime, drink plenty of water and abstain from sexual activity until clear