Sorry to hear you're having problems. It sounds to me as if there is inflammation, which could have happened because of something you ate or a stomach reaction (gastritis) which generated more reflux. The Nissen does not eliminate all reflux...just brings it down to a normal level. It is possible to get a flare-up from time to time.
Try not to panic. It's not a bit likely that you've done anything to your wrap. As I recall, I had a similar situation at about 8 or 9 months post-op. It lasted a little while, then resolved itself. I have always found that Carafate Suspension works extremely well when my wrap gets irritated. It coats he esophagus and stomach and helps things settle down.
This is a prescription drug, and is quite expensive, but if you have good script insurance, it's worth the money in my estimation. I actually keep it on hand all the time, as I have a reactive stomach. If you don't have good insurance, you could try the generic tablet form and put it in a medicine cup, add a little water, then throw it back like a shot. It's no as good, but definitely helps.
Be very careful what you eat while you're healing. Stay away from rough, acidic, or spicy foods, as you won't want to irritate your already inflamed esophagus and wrap.
Is it possible that a medication you're taking got stuck at the wrap site and irritated the area before getting through the wrap? Sometimes food, drink, or medication can sit at the wrap and cause irritation as a result. Let us know how your tests go...
Words of wisdom by Eckhart Tolle:
"Whatever you fight, you strengthen, and what you resist, persists.”
“Worry pretends to be necessary but serves no useful purpose”
“Accept - then act. Whatever the present moment contains, accept it as if you had chosen it. Always work with it, not against it.”