I found a small lump on the back of my sons head when he was very young, like a few months old. His dad and I looked at it and checked both side and our own heads and noticed we all have small lumps in this area. So even though his seemed like his was possibly slightly bigger on one side, his dad convinced me it was no big deal. He is now 1 1/2 yrs old and I have found a much larger lump in the sane are, I am quite positive it is the same thing I found when he was much smaller, only much bigger in size. What could it be? And, what should I do?