Recently my lower back & sides pains from inside when period start .it goes down to legs too. had to take a mild pain killer to keep it away. why ?

Painful periods: There are multiple options. Hormonal treatments such as birth control pills, Progesterone treatments and the Mirena (levonorgestrel) iud are effective reversible treatments that will help many people. There is also a drug called Lysteda that contains no hormones which will help others. If you are done having children discuss the option of an endometrial ablation. In some cases a hysterectomy will be needed.