Welcome to Healing Well! Have you discussed your continued symptoms with your surgeon? If so, what does he/she say? I don't have any first-hand information about this surgery, so I can't be of much help. However, I can say that with Nissen surgeries, symptoms often take some time to go away. I'd be interested to hear what your surgeon says.
Unfortunately I did have a friend who had her gallbladder out, and continued to have the gallbladder "attack" pain even when it was gone. She ended up trying stints to stretch the duct, and it didn't help. She finally decided that she would just have to work on maintaining a trigger-free (or low-trigger) diet.
I wish I could be more help! Hopefully someone with more experience stop by to respond to your post soon.
Again, glad you've joined our forum!