This is a tricky subject with a lot of factors that may contribute to you getting smacked. Lots of good suggestions here for ways to fix it. I would also consider the following-
Perhaps the comb shape is odd. Is it thick or thin or in between? Thick combs can lead to rolling your head and contribute to cheek slap.
The stock does look to have an odd shape with the nose of the comb being quite high. The comb is quite steep with 1" difference between the nose and heel. I would reduce the comb height towards the nose and leave the drop at heel the same as it is now but heed Chuck's comments above.
The pitch looks strange also as the LOP to heel looks greater than the LOP to toe and the reverse should be the norm with a slightly more prominent LOP to toe.
I'm guessing that the combination of the comb angle and pitch angle are causing the gun to rotate excessively on recoil.
Remember that reducing the LOP will also reduce the drop at face as your head will move forward on the stock.
