I would try a paed chiro or cranial osteo as a PP suggested. DD1 had an awful flat spot - same deal with her ear etc. She could not turn to one side at all this meant that no matter how hard we tried to encourage turning/stretching she just couldn't. At 4 months we started seeing a chiro and within 2 weeks we saw a noticeable change - at 3 months you couldn't tell. I was referred by a fab MCHN - was the best thing we did. Good luck - perhaps ask around for someone????
PS I was very sceptical and was keen just to get it fixed (re helmet). Good luck and keep persisting if you are not happy.