I had a huge sterile abscess in the same exact spot
Prop double yours,I got from injecting. 3ccs of synthol in my delts and I didn't even realize it was there till some girl that was in the pool with me at my shore house years ago and said something is wrong with your delt,I said it was muscle but she said that's def not muscle,when I went home from the shore house and looked in the mirror my delt was use I stuck a huge needle deep inside the muscle and darned 30 cca of puss out of it but I always do crazy shit like that.
Another example I caught MRSA which is a flesh eating bacteria from. My gym
I had huge red lumps all over both arms they were the side of prunes.
I sterilized a knife cut them up and squeezed out so much puss from all of them when I went to the ER they asked what doctor drained them I said I did it myself.
The doctor said I'm not supposed to tell you this but you did a great job.
Then they gave I.v antibiotics and I was done ,my girl caught it from me but she had a huge one on her ass I told let me drain it or the doctor gonna cut it put drain tubes and you'll have to keep coming back she said I'm scared she regretted later when she had drain tubes in her ass after ther sliced her really bad and had to keep going back for weeks and I didn't need any follow up appts