Do I need a personal injury attorney for an accident I had?

I was compleating a merg at an off ramp from the freeway. A semi hit the rear left corner of my car, police report states he is in violation of VC22350 unsafe speed and not paying attention but it states that I was an associated factor because of VC21658 because i was merging. If he would not have hit me I would have been fine and the accident would not have happened. My car was totaled, some B.I and I was pushed into the car infront of me. Now the other party's INS Co. is refusing to settle and is investigating because they say I was at fault too. I am starting therapy for my back I have no car since 9/18/09. They are claiming they are not responsable, should I get an attorney or should I continue to do this on my own.