It's fine. It's normal. I have learned through here that some shampoos attract kitties. I suggest to switching shampoos if you dont like this behavior.
They dont like Lemon scents. You could just kind of let the cat know that it bothers you, or move his head. My cat gets so much into smelling my head, that he burries himself in my hair, and falls alseep. I love it. Sure, it may get annoying after a while, but he loves you.
He's just smelling you, and making sure your still the greatest person he's ever met.