What could this be?

My left boob is in SO SO SO SO SO MUCH pain i cant even describe! Its causing the lower part of my left body to hurt when my boob is in pain. When I walk, it hurts, when im laying down , etc. The right boob doesnt hurt at all, just the left. It hurts almost all over , but mostly the side. I read online that this can be an early sign of breast cancer, but I am only 16. My period does start very soon, but I have NEVER in my life experienced pain quite like this before. I have had my period since i was 8 , so breast pains before period isnt new to me, but this pain definitely is. Thank you