Talk to Pediatrician on Rubs Penis

Its been a year my son lays on his stomach on floor or bed and rubs his pennis against hard surfaces, uper neechy hota rehta hy musalsal, makes strange voices like pleasure, jab men seedha karti hon to face red hota hy r pasina aaya hota face pe kafi r pennis erected hota, men pyar se ghussay se mar k dara k her tarah se samjha chuki hon but wo nahi chorta aisa karna, kbi pant utar deta hy r floor pe lait k penis rub krta jb wo 2 sal ka tha tab se aisa kar raha hy, men boht pareshan hon is sab se, aisa kiun hy iski kya reason hy?