I have a tender lump in my upper arm muscle that feels to be about the size of a small pea and moves upon palpation (although it is painful). I first noticed muscle pain upon stretching two weeks ago, and the muscle pain has been consistent both with stretching and to touch.. Tonight I noticed the lump. There is no visible bruising, no bites or stings, and no recent injury to the area. I am 52, female, and technically obese (although I am successfully losing weight on Weight Watchers). Should I follow up with my doctor or wait a bit more? Thank you.