Is The Penis Size Normal?

Hi, I am a 16 year old male, and since starting puberty at the age of 14 I ve developed a lot of pubic hair and some facial, chest and armpit hair, however my penis hasn t increased I m size. When erect it is 5 inches and when not 3 inches. Is this anything serious? Should I see my local GP? or is it normal? It s just embarrassing as all my other friends have fully gone through puberty and I m lagging behind. I had an operation when I was younger for cysts on my testicles, does that have anything to do with it? Thanks.