JustForInfo, acne is often caused by the same hormones that cause ovulation and menstruation. It does not happen to all women, and different women can get it at different times of their cycle (just before period, during period, after period, around ovulation). If it is a big problem, birth control pills are normally prescribed by a doctor to control the acne outbreak.
Don't feel guilty about masturbating. It is something totally natural and private. You will be surprised to know how many other women around you also masturbate.
It is also one of the best ways to learn about your own body and sexuality and a totally safe way to work off your sexual tension during puberty. Remember to always wash your hands and do not use anything with sharp edges or splinters to masturbate with. And once again, wash everything touching your genitals to prevent getting an infection.
Take care!