Been having abnormal bleeding for a month now, due for next period in three days. What could be wrong?

Need to consult a. Doctor. Bleeding for month warrants evaluation by a doctor, please see one at your earliest convenience.
See your doctor. Symptoms and concerns like these mandate a thorough evaluation by your doctor. Only after such an evaluation, which may include labs and radiographic examinations, can he/she let you know what's going on and how best to help you.