Hi Choosingjoy,
What a great username! Welcome to Healing Well! Many here have had the Nissen surgery, so I'm sure that others will be by to share their experience with you.
You are very right that it will take 6-8 months to do most of your healing. Actually it will take a full year to completely heal. I recently realized that I also continued to improve during the second year.
There is one thing that might be helpful regarding "heartburn" feelings in your esophagus. The esophagus is not a smart organ, and can not diffrentiate between types of pain. If you get any pain at all in your esophagus, it sends a message to your brain saying "HEARTBURN!" Because of this, any heartburn feelings you are having are not necessarily caused by reflux.
Since you are healing, and there have been a lot of changes made to your upper GI tract, you will certainly experience pain. You're still relatively early in the healing process.
Here's the deal...it is very likely that your wrap is holding some of the food and liquids you are eating back, and they are sitting at the wrap site, formenting and creating a pain and burning sensation. Many on this forum have experienced this. If your wrap is fairly tight, often everything you eat and drink doesn't make it through.
Even now, (2 and a half years post-op) I can get some backup...nothing troublesome, but I have to remember to drink extra liquids after eating.
Also, if you're taking pills, they can often get stuck in the wrap or lower esophagus and cause burning to occur.
I can't tell you for sure that these things are causing your problem, but they are common culprits and it is a likely possibility. You are still in the early stage of healing and things have not settled completely into place yet. It all takes time.
Keep in mind that your surgeon was paid the big bucks, and should be available to answer any questions or worries you might have.
I expect others will be by soon. It's a holiday weekend, so many are extra-busy.
Again, I'm glad you've joined our 
Wrapped Club"!
Take care,
Denise