Disclaimer: I'm not the type to run to the doctor "just to be safe".
My DD had a big bump on her chin for over a year. It has finally gone away. We knew how it happened (although I have forgotten now) and we treated it holistically. It was under the surface of her skin and was not a pimple or ingrown hair or anything like that. I vaguely recall a fall.
Anyway, I use a variety of "sensors" to determine how to move forward. First, ignoring my "mommy fears", what is my gut reaction? Does it feel serious or minor? Second, how is my child reacting/acting? Aside from trying to "flatten out" his bump, is your son acting normal or is his behavior "off"? Third, if I am just not sure, I ask other parents and/or an advice nurse. Seeing it in person is far better than over the internet or phone, so I ask my neighbors or playgroup parents (etc). A call to the advice nurse is usually more for confirmation and instructions versus "should I bring her in?" If I ask that question, the answer is always yes.
My last call to the advice nurse was, "My daughter fell and hit her head. I heard that awful THUNK and she cried immediately. It has been a few years and I have forgotten the signs of a concussion. What should I look for?" The nurse asked a few questions (how high was the fall? what surface did she hit? how old is she? etc) and determined it was a gray area and told me the signs to look for. DD started acting oddly and we started packing up to go to the emergency room, then DD started vomiting. Grabbed a bucket on the way out the door.
