they don't always work, and don't last forever, injections are more for swelling based pains.
I had one, it didn't do a thing ..... just to add when they did mine, I was laid on my back, my head taped down facing to one side, I had a CT scan at the same time (to judge placement and depth of the needle), they inject, then scan, put it in further, then scan, then go all the way (they need to see for accuracy), even though I felt like I had been abducted by aliens (because I had no prior knowledge), there was very little pain, I did feel woozy, (just at the thought), but it all went well, I expected way to much and had no results whatsoever (it takes up to a week to take effect).
I'm sharing this just to let you know my experience, so you know what to expect (or not), I'm glad I didn't pay for it, as the whole thing did nothing for me .... but it's an interesting conversation at dinner parties..... I really expected them to lay me face down (nope), I expected the needle through my back (nope), they went in through the side of my neck ........ again, even though it sounds quite graphic, very little pain ..... and for you, it may just work .... good luck