I’ve been having pain and soreness under my armpits, it started out as the left and then some days its the right and some days its both. The day before the pain started I was being lazy and tried to stay on my bed while stretching to reach for something very far and low. (I don’t know if it’s an over strained muscle or something else) That was two weeks ago and some days it still comes back up and hurt. The pain starts from under the center of my armpit and travels up the edge of my arm and some times it stretches towards my breast. I have no discharge from my breast or any lumps but I’ve been silently freaking out each time the pain starts up again. I’m 17 by the way. Any idea what it could be?