I got news for you: yes, you will need to hire a disability lawyer.
Here is how in my state, according to my Doctor and SSD office:
When i asked my Doctor if i can go back to work he suggested to wait and see how will i recover. He has experience with his patients when they go back to work and than realise they can't work due to pain and a lot of problems - than it is very hard to go back on disability, especially if this more than 60-90 days since you went back to work.(depends on a state rules).
Usually it can cost here about $5,000-8,000 to pay a lawyer to work on your case and he never promisses that case can be win. Also your Doctor can determine your problems and help with your case.
I don't believe that your Doctor is right about pain is not a reason for you to get disability. Besides that pain is usualy an indicator that something is wrong, you had fusion surgery and a lot of people have problems after this for the rest of their life. I personaly was told by Doctor at HSS in NYC that i can't expect to leave without pain for the rest of my life and second surgery will not help my situation anyway.
I really tried so hard to do everything in my power to get better and go back to work, i had an excellent job. But i can't seat for long, stand or walk, i got nerve damage in my legs/feet and to be very realistic i know if i decide still to go back to work it would not last for long. At least for now.
Good luck to you and i hope you will feel better. Take care of yourself.