I have been bleeding for 18 days now im done but feel like im gonna start again cramps pain in lower back and cramps in legs?

See a doctor: If you are sexually active, you may have had an incomplete miscarriage or an iud that has dislodged. Infection, a fragile cervix, fibroids or tumors can cause bleeding. You also may have "dysfunctional uterine bleeding", cause unknown. Progestin may be used to stop uterine bleeding acutely. See a gynecologist asap. You may need antibiotics, ultrasound, biopsy, or a d&c.