I started my period. I am not currently taking birth control, but I have norethindrone 5mg from before. Can I take norethindrone to stop the bleeding?

Sure, may not work. Once you have started your regular period, it is difficult to stop it. Hormones such as norethindrone are used to alleviate heavy irregular bleeding, but in higher doses. This too, may not always work, or it may take some time to work.