Sorry to hear you've having problems again. As Bill said, you can still get some reflux after a Nissen, so it doesn't mean your wrap has failed. It seems that your barium swallow will be concluding that as well.
Antibiotics can certainly set off your stomach, and create some resultant increase in reflux ymptoms. I try not to take ANY because I always end up with a bout of gastritis, and gastritis can increase reflux episodes.
I had my surgery over three and a half years ago, and because I have asthma and am extremely sensitive to ANY reflux, I my allergy/asthma doc wants me to continue to behave as if I have reflux in a couple of ways...I continue to take a PPI before dinner, and I sleep with the head of my bed elevated. Better safe than sorry.
If you're having a bad time of it, you might consider adding some acid suppression to your routine for a couple of weeks until things get feeling better. Be careful of what you eat. Don't go to bed with any food in your stomach...wait 3 to 4 hours after eating. Consider elevating the head of your bed again.
Once things settle down you can gradually get back into your more regular routines, but continue to watch out for reflux triggers.
One other thing to consider. Quite often after gallbladder surgery, people can get excessive bile, and even bile reflux. Bile can create all kinds of stomach discomfort as well as nausea. I don't know if that could be part of the equation, but you could discuss it with your doctor when you meet about the barium swallow results.
Don't panic. It's very likely that you will get things straightened around and back to normal. Can the wrap stretch over time? Yes. But it is intact, and that's important.
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.”