Since this was a rear end accident, why are you claiming against your own insurance coverage?  The other driver's insurer should be covering all damages.

Regardless, if you can't convince either insurer that a particular issue is the result of the accident is as follows:  (1) in the case of the other driver's insurance, you'll have to sue the other driver and prove your case to the satisfaction of a judge or jury; (2) in the case of your own insurance, you'll have to sue your insurer and prove your case to the satisfaction of a judge or jury.