Suggest Treatment For Persistent Pain Caused Due To Multiple Sclerosis

My pain doctor that I've been seeing for 5 years or more for my MS and continued pain. Has just starting doing weekly injections on / in me to take away the pain. Today, which is my second time doing the injections I was more informed as to what was going on; And he also injected air into me and I did know about it and he has been seeing me monthly, sometimes more often. Has anyone else heard of this type of procedures? Am I going about things the correct way, I do trust my doctor him 100% and do have faith. Please advise.