HELP!! I was involved in an auto accident in August.?

I was at a stop light and was hit from behind . Didn't feel hurt, so we exchanged information..Four or Five days later I started having muscle spasms in my lower back area. And I didn't attribute the pain to the car accident, but later the pain was more frequent by the days and now consistent. I went to the my doctor and he did xrays and determined that it was possibly from the accident. I have never had back pain before. The insurance company told me to fax all of my medical and time off info and they would access the amount of damage. I am using my health insurance to get this treatment. Is this okay, or should I call my agent and have them refer me to a therapist that would bill them? Because the therapist that I am now seeing does not honor 3rd party billing? If you know of a Physical Therapist in FT Worth, TX, Please let me know....