I've had pain in my left upper arm for the last month that worsens with activity. recently while rubbing the area, i noticed a lump in the muscle that feels like... chewed gum. the pain worsens when i rub the knot. same issue in my left thigh?

This is possibly a distortion of the fascia Fascia is a series of tissues like bands under the skin in bery long and wide layers. Also, fascia is arranged likre tubes around all the muscles. Some small damage can cause a smsll portion of the fascia to become a lump. Find picturs of fascia on Google, etc. Treatment woulld br a rubbing. Fimd a doc to rule out a serious problem. Then, find FDM.com

Sounds like one has issues with tissues and tendons. They feel like "chewed gum" because they are softening and weakening. Trauma and overuse or strain could contribute to it but most of the time it is due to diet lacking the "Connective Tissue" nutrients that are found in Bone broth and things like celery & broccoli. If one has not seen a Doctor recently, a visit to the PCP might help.