Flat Spots on baby's head at 4months? Help

This is a concern with the back to sleep programme designed to prevent cot death. Please chat to your paed about it. In sever cases they put a special "helmet" on the childs head to try and get it rounded again.

www.babycenter.com/0_plagiocephaly-flat-...-syndrome_1187981.bc

My son is now 4 months old and was a prem baby, he refuses to sleep on his sides and no matter what i do - he just wont. I even bought this pilliow thingy that keeps them on their sides and then just end up with a very irritated young man that will scream blue murder until he can be on his back as desired. His back of his head is so flat, and even tho there is no medical concern - I simply cant take it anymore, it makes me constantly think something is wrong- any advise would really be appreciated. He does have plenty of "tummy time" but he sleeps thru - 19h30 till 06h00am. How do i try and fix this? or will it come right on its own?