2 year old headbutting

[Izzywizzywoo2016]

My 2 year old son has been headbutting. Wether its the floor, sofa, radiator or even me and his dad he constantly does it. Today he was sat on my lap and just head butted me in the mouth for no reason, so i told him no and sat him out. Then asked him to say sorry and he gave me a cuddle etc. but 5 minutes later he headbutted the sofa (hard bit aswell on the arm) and i told him not to do that but he just laughs. Last week he head butted me in the spine and it left him with a bruise on his forehead. My back was in agony. Id not long broken my spine too so its still very sore. That day i put him in bed because i was quite mad and he just laid there and was not bothered what he had done. Any ideas on why he does this and how to stop it? I feel like im failing sometimes and i dont want him to hurt himself i worry one day he will headbut something really hard. I have a 2 year development check coming up soon. I will mention it to them but in the mean time any help would be good. Also iv been told 'its just a stage' they grow out of it. But its been a while now xx