I cannot confirm anything without examination but it can be a cyst, Boil, benign skin growth, wart or even a malignancy cannot be ruled out. Cysts may occur anywhere on body but scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts. Blocked sebaceous glands, swollen hair follicles and excessive testosterone production will cause such cysts.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I have had very much the same symptoms. I have extreme fatigue and require a nap in the afternoon just to recharge due to being completely drained. I also have a history of tachycardia and lately over the last couple of months I don't have SVT like I used to. I do feel my heart jump into arrhythmia many times a day. I have had cold symptoms for nearly 6 months with swollen, hard tender nodes in my throat and underarms ( especially left side) and very tender on ribs below left underarm and left clavicle is invisible now due to the swelling in my left chest area. I have also gotten super light sensitive and my eyes hurt/ burn constantly even closed. My body never seems thirsty and I have to remember to drink fluids. I also vomit if I even drink a small glass of wine or 2-4 oz of beer. I'm pretty anxious. Are you feeling any of these other symptoms?