From your symptoms, it can be due to metrorrhagia(heavy periods). Various factors causing it are endometriosis,ectopic pregnancy,hormone imbalance,endometrial hyperplasia,polyps,use of IUD’s and depo shots, sexually transmitted diseases,PCOS and benign and malignant pathologies of the uterus.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
If you have only gone to your doctor once or twice for this lately to try to get help, go back and look for some answers and treatment. If you have gone frequently and they have only put you on the one drug, get another doctor! You need proactive help for this! If you can, go to a gynecologist, not a GP, as they are focused in this area and will be better able to help you.