I had a fusion at L5-S1 about 2 years ago and am still in really bad pain as well. I am pretty surprised that they told you to go back to the gym after only 3 months. I wasn't even able to bend for the first three months and then only started physical therapy after that. My next disc is now bulging, which is why they think I am still in pain. My advice would be to get X-Rays and possibly an MRI done to make sure that the healing is progressing correctly and there hasn't been other disc problems due to the extra strain on your surrounding discs. What I have learned is that my body is usually telling me when to stop, which is when I hurt more. I would not push yourself too hard for now. Walking and stabilization are the two things I would work on if I were you. Stabilization can be done in a very controlled way which is key for me since 1 wrong step can affect the way I feel for days.
Is the pain actually on your spine area, or is it more in the muscles on the right side? I hope you can find some relief!
HI and welcome to the back and neck support forum.
I wish I had words of wisdom for u, hopefully another member with a similar experience will add a comment.
I wish u all the best.
"selma"