The usual procedure is to try all conservative treatments before having any surgery. It appears that you have done that for 18 weeks without any success in relieving your symptoms or the herniated disc shrinking.
Your next step would be surgery.
I have not heard that the longer you wait, the more likely the herniation will not shrink
It is true, though, that the longer you wait the better chance that there can be nerve damage. The problem is that no one really knows how long is too long and it is individual with each person.
You should always have, at minimum, one other opinion before having surgery when it is an elective surgery, especially when it is spinal surgery.
i would not suggest that you have another opinion based on just sending MRI pictures to another spine surgeon.
An MRI is only a small piece in the picture of a proper diagnosis and course of treatment. A good spinal surgeon will not only want your MRI pictures, but any other tests you have had done and they will want you present as well. They will examine you, check your symptoms, listen to what you say about your symptoms and then proceed to match your symptoms to the MRI pics and any other tests you have to make a proper diagnosis and treatment suggestions.
You do not have to see a neurosurgeon for another opinion. You could see an orthopedic surgeon who specializes in spines. They are just as capable as a neurosurgeon in doing spinal surgery.
I personally prefer an orthopedic surgeon. I have used one for my spinal surgery and found orthopedic surgeons to be far more up to date on new procedures and doing far less invasive surgical procedures as well.
Has your doctor discussed in detail with you the surgery that you would have? What he would do?
Just saying discectomy doesn't necessarily include everything he would or would not do.
Has he mentioned a microdisectomy, which is far less invasive, smaller incision etc.
The success rate with a discetomy/microdisectomy is very good.
I would strongly urge you to get another opinion, actually several before undergoing surgery and have your present doctor go into detail about what surgery he is saying he would go.
good luck
Fran