I haven't started my period because of stress, is it okay to start my birth control?

May not be stress. There are many causes of a late period--from hormone imbalances to pregnancy to stress. Don't assume that it's stress without getting it checked out. If your menstrual cycle is late, early, or heavier, your body may be trying to give you a message. Do a home pregnancy test, then confirm with your doctor that they recommend going ahead to start taking the pill.