Pimples and blackheads are very common in puberty because your hormones are stimulating your skin glands to produce more oil. They can appear closer to your period as well, due to hormonal variations. Don't despair and, most importantly: avoid squeezing them! This can cause scars. Wash your face gently twice a day, use proper products, and remember that this is just a temporary phase of your growth. Your beauty and value go much deeper than your skin!