You are only 4 months post spinal fusion, I do not know if your Doctor told you, but recovery from a fusion takes about a year, and that is full recovery. I had a 3 level/360 fusion in 07, and it took a year to determine that the surgery failed, due to the cadaver bone that was placed on my fusion that started to fall apart, so for me it was kind of a defective product issue, but before surgery my surgeon warned me that spinal fusion recovery was a long haul, and to be prepared for it.
The best exercise that you can do is walking, I started very slowly, a few houses down at first, then to the corner, half a block, etc. until I reached 5 miles daily, and this was with my cane. If you still have nerve pain after a year post-op you might want to ask your pain management Doctor about a spinal cord stimulator (SCS). I had my SCS implanted in June of 08 due to nerve pain down both legs, and the device was my salvation. It took away my nerve pain 80%, and it has made my life more bearable. The one thing that the SCS does not take away is the mechanical pain, for that I still take pain medications, and will probably take them for life. I don't see it as an issue, I have a condition called Fail Back Surgery Syndrome, and due to FBSS, I have to take pain meRAB, just like the person with diabetes, or heart disease that has to take medications for the rest of their lives, I am going to have to do that for life.
So like I said, you are early out from surgery, start walking, and try to keep a healthy diet. If you smoke stop smoking (I did smoke and stopped post fusion), and be patient, I know that the pain sucks, but a fusion surgery is complicated and it takes a long while to recover. Take care, :wave:
Tipper