People experience the lead up to their periods (pre-menstrual symptoms) and period (menstruating) differently.
Some people can get cramps or other uncomfortable symptoms a week or two before their period begins (PMS) and during their periods (menstruating). This is typically due to the hormones your body releases in the lead up to and during menstruation, that cause the uterus to contract so it can shed its lining.
Some amount of discomfort – like stomach cramps, backache, headaches, acne, feelings of sadness or anxiety are common.