Yes, ask your MD to get pre-approval from your insurance company. Most of the claims get denied due to insufficient documentation or coding errors. Keep a file with all your test results, especially if you change doctors, because records get lost.
Are you asking to get pre-authorization after the fact? Meaning you had the injections in July without preauthorization? If so that may be a problem. Usually someone at the doctor's office helps out with pre-auth. If you are asking if you should get pre-auth before another injection check with the insurance company to see if you need it. The office staff should work with you to help secure it.