Why does hair grow faster on one side of my head?

I try to take good care of my hair. I wash it 1-2 times a week, i condition it, I make sure i spray a light oil sheen on it to keep it mosturized, I get my ends trimmed and I wrap it everynight. One side of my head has grown nice and long but the other side is sooooo much shorter and dryer! I keep applying oil sheen to it and i make sure it's trimmed but it just won't grow! What am I doing wrong?! :(