I've had about 9 sets of these, with multiple injections each time.
The effects varied. The anaesthetic used in the process soon wears off.

I found that I had an average of about 6 weeks benefit, variable though it was, from the injections. Sometimes there was very little gain.

You really need to get to the cause of the problem, and then see what can be done.

My big breakthrough came when I was found to have very tight neck and back muscles, which were applying a lot of pulling to my neck and head, hence the headaches.

Massage gave instant relief, though not long lasting. Still, I had them regularly for over a year.

Then I started taking magnesium chloride, mixed with water, and that quickly cured me. Best thing I've ever done!

Several years later I am getting a constant dull neck ache, and a bit too much use of my arms results in pains over my neck, shoulders and arms. I believe it is DDD.

I'll be going back to my physio next week to get some neck exercises to help.

With your injections, it may take another try at different locations. They have to target the exact spot.

You could always try a physiotherapist in the meantime and see what can be done physically. Your lifestyle (read computers etc) may be a large factor.