Age 19 why are my breasts sore? mostly on the outer side near armpit. i've been working out a lot lately. they are tender when i touch or lay on them.

Sore muscles: Breast pain can come from multiple sources. Sometimes this pain may be related to the end of menstrual cycles. If you are doing exercises that stress the muscles of the chest, namely the pectoralis muscles, you may feel pain across the chest that extends into the armpits. With fluid hydration, rest and anti-inflammatory medications, you may be able to find relief from your aches.