My menstrual cycle came early and my flow is heavy. i'm also having lower back pains, fatigue and nausea. what could be wrong?

Painful,heavy period: First start with a pregnancy test. If negative, this can be a variety of things including fibriods, endometriosis, dysfunctional uterine bleeding, or even pelvic inflammatory disease. Usually your doc will take a complete history, do a pelvic exam, and will consider an ultrasound. Treatment, like most things, depends on the cause of the painful, heavy periods. Best of luck.