I really hope it doesn't take an entire year, or 9 more months, as it's already been 3 months. I keep getting mixed answers when I ask my doctors, just that "nerves take a long time to heal."
Not to take away from DR. Kokil's excellent answer, but I will answer the specific question in the title.
If the pain is indeed caused by the injection, and subsequent localized damage, it could take up to as much as a year to heal.
That's not to say it will, but that would not be abnormal. Also, that doesn't account for any conditions referenced by Dr. Kokil.
Hi!
To treat this pain, you have to first confirm it is sciatica. You need a MRI of lower spine and nerve conduction studies to rule out pressure on nerve and nerve damage.
If this is indeed the case, then yes, nerve block may help. If there is some other cause of your pain, then the nerve block may not help. The pain can also be due to blocked arteries or due to spondylitis of lower vertebrae. In which case the treatment will e different. You can try physiotherapy and acupressure etc. Please discuss with your treating doctor. Take care!