For the past few days, I have noticed certain spots on my shins and both sides of my arms between my shoulder and elbow have very tender spots on them, almost like a bruise . It isn t a bruise because i have not had any type of accidents like bumping them on anything. There is also a pea sized knot under the skin on the right arm between shoulder and elbow, i pushed it in and it made a popping sound, the knot went in deeper to where i cannot feel it anymore. After i pushed the knot in, there is a noticable indention in my arm.