Welcome back, hon. It's good to see you. Though I'Absolutely it's OK to do that. It might take them a day or so to get in touch with the doctor to get the refill OKed and so it's better to go ahead and call it in early.
Listen, if you're worried about the pain doctor using a needle on your back, or manipulating (popping) your back, then you're worrying about the wrong things. They seldom do either one of those things.
Pain doctors usually are just doctors who study how best to control pain. He would probably just review your medcations and then prescribe you some better meds. That's all.
And, you absolutely have veto power over any procedures. If he does want to do injections or something, just say no. Explain that it scares you. You won't have it. Period. They cannot force you to have any treatment modality. OK?
So go see your pain doctor. I think you will be pleasently surprised. And if you're not. Find a different one that you do like. There are a lot of pain docs.
Healing hugs and lots of love,
Dan