After 12yrs of training hard amost non-stop I have begun to fall apart. Knees hurt so I can't squat heavy. I have golfer's elbow and my rotators hurt so I recently started training with 10-20lb dumbells. I thought this light training would fix me up but ever since doing side laterals with 10lbs last week, my left side deltoid has a big, hard, sore lump in it. It doesn't interfere with mobility, it's just swollen and tender. I've never had this before. Anyone have any idea what it is?