My baby girl is just shy of one year old and she did the same thing, only she turned to the left. I learned that if I gently turned her head to the right (while she slept) and held my hands there for a short while (surely no longer than a minute) she would stop trying to turn back to the left and go back into a deep sleep. Some days I even woke up with her head still turned to the right.
I typically get up to use the bathroom at night, so I would always check her and turn her head. It did take several days before I could turn her head and she wouldn't immediately turn back though, so while researching all the other stuff you may just want to keep trying to gently turn his head to the left to see if eventually he'll be OK with it. Incidentally, my daughter's head looks fine to me and now that she can turn over her preference for looking left is all but a fading memory.
Good luck. (by the way, SIDS is a much greater concern to me than a flat head...so make sure you understand the risk before you put your 7 week old on his tummy.)