What Causes Roundish Spot On The Back Of The Head?

My son is 11 1/2 years old and about three months ago I noticed a roundish spot on the back of his head near the occipital bone area that is seeming to be losing hair/or hair is slightly lighter. I touched the area and it is kind of squishy. My son says it doesn t hurt to touch it. My son also is seeming to be very hungry all the time. I may be over reacting but I just want to make sure it isn t something . He has not had any injury to that area either.