Can we sue the driver of a car that was at fault? Allstate says the injury was not that bad and wants to settle for $650.00

The accident was caused by the driver of the car my son collided with. The insurance company adjuster for Allstate indicates that there were no major injuries sustained in the accident for him to provide a settlement. We could not get a rental car from them for more than 1 week and when we finally got a rental car, they instructed the rental car company to ask us to return it before a settlement was made for the total loss of his vehicle. Also, to this date, Allstate refuses to pay the medical expenses incurred unless I settle with them. Allstate has offered to settle for $2,500.00 but that is only going to pay the medical costs. Also, the adjuster calls this a "routine" office visit and there should be no additional money paid out. My son, who is 18 yrs of age, is having problems driving, especially in traffic. He refuses to go seek more help in overcoming the traffic fears and the adjuster doesn't believe this is an issue created by the other person he ran into.