When you say you're belching, are you making yourself do it like you did prior to surgery? Do you think some of it is habit, and you find some relief from doing it?
If the burping is automatic and you don't have any part in the action, then it's more typical of the "stomach burping itself", which is common after Nissen surgery. I can burp, but I don't have control over when it happens. I can feel it coming on, but can't make it happen the way I did prior to Nissen surgery.
It seems to me that perhaps it's something you're used to doing, and as you say it's hard to get it started, which is because of the wrap, but you can force it out. Perhaps you feel the need to continue burping, and somehow have figured out what most of us haven't...how to burp at will.
Here are a couple of links to website articles you might find interesting:
I hope you get it figured out and can get some relief. Have you discussed this with your surgeon and/or GI doctor? Perhaps there is something they can do for you.
Nissen Fundoplication 2/09
Allergy/Asthma"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.”