Car accident: How do I know what I am entitled to?

I was in a car accident last September. I'm trying to avoid seeing an attorney. It was the other party's fault, their insurance paid for my medical bills, which exceeded $3,000. I wasn't seriously injured, but I had to go to physical therapy--I stopped because I was in another accident. The first insurance company is offering a settlement which is similar to the figure my medical bills totaled to. I have been hearing that the medical bills should be multiplied by 2 or 3 and that is what I should receive as a settlement. I have no idea what I should ask for. Any advice is greatly appreciated!