I wanted to comment in this threrad a while ago but never got around to it. When i was about 12 I noticed some lumps under my nipples. No big deal...Doc said that it happens during puberty and will go away. Well a few years later, they are still there and they are painful to the touch.
I go to get an ultrasound done and find out it is fucking breast tissue! This is in my mid teens. Doc says it isn't bad enough for surgery and wants to see if it goes away and runs some blood tests. Sees that my LH and FSH are really low. He concludes that I am just hitting puberty late... and foolishly we never followed up.
Fast forward to two years ago. I start getting some really strange symptoms. Hot flashes, headaches, lethargy, very moody, depressed, can't gain weight, no libido.... I get some hormone panels done and have an MRI done on my head and find out my pituitary gland is all sorts of fucked up. And had I known that years in advance, I would have never been through the shit i had to go through.
So, bottom line, get your son tested by a good endocrinologist and make sure his hormones are normal for his age. If so, it might just go away, and if something is wrong, you can treat it before it gets out of hand.