Oh that's great news! I'm so glad you have a good doc. Those things do sting, and that's putting it mildly!
When I was getting mine I think 3 injections/year was the limit, but I could be wrong. If the first one didn't work, I'd go back for another. When I started having them in 1986, they actually did them in surgery rooms between surgeries and would knock you out for them! Those were the good ole days! Didn't feel a thing.
Then insurance came along and said, "Hey, these people don't need to be numbed up for this stuff, they can endure the pain."

I was not a happy camper when that happened!
And yes, those shots can last for a long time. I know my SI injections are often very successful for a good length of time.
Keep us posted!