What Causes Skin Dehydration On Left Side Of The Head And Neck?

I have lines in my skin that appear to be from aging but are only on the left side of my head and neck. Specifically, a 45 degree line on my forehead, on the side of my cheek, and lines around my neck. My skin just seems extremely dehydrated..but only on the left side of my head and neck. The line on my forehead is caused when I sleep on my left side. When I wake up there s a crease on my forehead. I ve tried Botox and it didn t help. Why would this aging or dehydration happen only to my left side?