My period is not predictable. i never experience cramps but i now they are very severe and continue throughout the whole month. why? and what canido?

You need evaluation: That is a great question, but the answer is complex. The cause of your change in menses is due to a change in your hormones. It will depend on when you started menses (menarche), if there are other hormonal changes going on now too, weight changes, dietary changes, excessive stress or exercise and the list continues. With a good evaluation your medical provider should be able address your concerns.