Sharp burning shooting pains in breast/underarm that only disappear during my period - ultrasound showed nothing (during period). what could be the problem? would birth control help? very frustrated!

Breast pain: You may have premenstrual syndrome manifesting this way. Try to reduce caffeine intake, try vitamins e supplement. Birth control pills may make it worse, but they make it better - depends.

Neuritis pain: This kind of pain has a nerve-irritation quality. If it is from cyclical hormone changes, birth control might help - but, I do think you need a clear diagnosis first, talk w/ your doctor. Regardless of the diagnosis, this kind of pain responds to nerve pain medicines - like gabapentin. An anti inflammatory diet (like a whole-food, low fat, plant based vegan diet) & exercise helps! avoid caffeine.

Fibrocystic pain: Bobcat: it sounds like you may have accessory breast tissue that extends to your underarm area. This is actually normal, but the waxing and waning hormonal changes throughout the month can give you some pain/discomfort as the tissue swells/changes. Have your doctor examine you for this as well as advice on managing fibrocystic breast pain.