Are you positive that your part has not always been like that? Have you always styled your hair the same way? Is there anything you are doing during the styling process that would cause it such as turning your head to each side during drying/styling?

I would not be too worried about it. Unless your hair feels thinner, I would not consider this a symptom of thinning hair. Since I started wearing my hair curly, as opposed to straightening it, and went CG, I have noticed that I have a weird part going down the side of my head. It is just an area where the curls separate. I have learned to style around this and it doesn't really bother me.

If your hair does not feel any thinner but it still bothers you, I would just experiment with ways to style that will fix or cover it up. Use a second mirror so you can see the back of your head when styling.