No period, no cramping but have brown discharge, lower back pain, moodiness, nauseous, what's happening to me?

If you had sex since your last period and missed a period by 4-5 days do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless you get a period by then. Use first morning urine and follow the instructions carefully. Wish you good health! If you do not wish to be pregnant, use contraception all the time, every time. Consider implanted contraceptive, or IUD.