It is because of the hormonal changes happening in your body during that time. Many women have changes like that. Some women will break out before their periods, some when it starts, some right after it ends. Just before, during and just after your period is the worst time in your cycle.

It is right at the opposite of when you ovulate when your skin is beautifully smooth, rosy and plump. It is the body's way to attract men when you are at your most fertile.