As my oldest is not yet 14 (she is only 11) I can only assume/hope it is like the one my daughter had when she was 3 in about the same place. Breast cancer runs in my family fairly heavily so, of course, I panicked wheen I discovered it while bathing her one night.
I was sent to a specialist by her pediatrician. I was told that cysts like this often form on again off again over the course of childhood. That generally they are not of a type to be worried about and go away on their own. I was told to watch it and if it seemed to have dramatic growth over a short period of time or the shape (feel) of it changed that I should have her seen again for further testing. As it went away without any changes in a few weeks, I didn't worry about it.
So, I would say watch it for changes that make it different from what your doctor described and then take him in. IF it simply goes away in a few days or weeks, then you know it was okay.
Good Luck!!! ;-)