What should you expect after someone hit your car from behind?

I have been a passenger in a car when we were hit from behind whilst we were stationary. I suffered an injury, the shock wave from the accident traveled along my seat and the injury that I have sustained from the initial first investigation that I have been injured in my pelvis and sacrum, I am in pain and I am on Tramadol 100mg , ibuprofen 400mg Co-Codamol.

I am in pain when lying down, sitting and when walking, going up or down stairs is painful. What could I realistically expect approximately for my claim?