Okay... my baby still have a flat head ...?

My baby had dificult labor with the succion cups, and they told me is head is going to come back round... i've being treating my baby with a physio... and now is a 6 months and he still have a flat head... i'm sooo scared i did what they told me make him sleep on is side with pervision i put him on is tummy i have him in my arms ... when we go out he stays in the car seat exemple shopping do you think thats why is still have the flat head... but we need to go out of the house right... i dont know what to do i seen my doctor and she says it going to come back round but it seems like theres no results at all... should i let it go or fight to get that helmet.. does anyone tried the helmet and how long does it take for it form round help me please...