Breast pain in left breast for 6 months. had a negative ultrasound. what could it be?? can't sleep on that side. too tender.

Caffeine, hormones: Many females have problems with caffeine causing breast pain. Sometimes breast pain is due an imbalance between too much estrogen and/or too little progesterone. At your age, cancer is probably not a concern. Try cutting out all caffeine for a month and see if this helps your breast pain. If that doesn't work, make an an appointment with an OB/GYN doctor.