Why has my penis grown fat.?

When i was 16 years old my penis was 6 inches long and like 2 1/2 inches around i'm 18 now and have recently measured with a waist band measurer..and I am currently 7 inches long and 5 1/2 inches around why is the daggum thing getting so fat is it normal or does everybodys grow diffirently im not sure this is legitimate just kinda pondering don't feel comfortable asking my parents lol..:/