I have a dull achy spot on the left side of my chest, sortof where boob meets armpit, extending inward a bit over the top of the boob. I somehow can t really tell how deep it is, like if it s breast tissue or lung tissue or what. Sometimes my left arm gets tingly or feels, like, weak. I notice it more when I m in bed and it never lasts very long but today, right now, the boob-armpit spot has been bothering me for like two hours.