I had my Nissen Fundoplication on the 15th of April of this year, so I am over 3 months post-op.
The first 3 to 4 weeks, your wrap will be swollen, and this could be longer if you are older. This is most likely giving you the feeling of a ball under your breastbone. Hang tight, this is not uncommon.
As for recovery, It is not uncommon for folks to go as much as 10 weeks to several months (4+) to start fully adjusting. Recovery is like a fingerprint, it is unique to you and different for everyone else. You are safe to go back to work when you feel you can work comfortably with minimal problems. But, like I said recovery is like a fingerprint.
I was able to go back to school after 1 week but not without pain and significant fatigue. I would have to frequently catch my breath in the hallways and walk slow.
Just take it easy and keep your eyes on the prize. The first few weeks are the weeks where anything can happen. You are recovering!
Stay safe and smart and good luck!