What you're experiencing is certainly not typical. While early swallowing difficulties are common, after two and a half months, you should be able to eat more normally.
Obviously, from the barium swallow info, you're wrap isn't allowing food through.
I agree, that it's puzzling that your surgeon would go forward with a full Nissen when your manometry showed swallowing issues. Most would have done a partial wrap at most. Someone with compromised swallowing abilities needs a much looser wrap to allow that reduced swallowing reflex to push the food through the wrap.
A dilitation would be the first step, from what I've read. If that doesn't do the trick, it might behoove you to get a second opinion from another surgeon. If you're in an area with lots of medical facilities, you may find someone else who is very experienced in the fundoplication surgery.
If not, you might be well served to take a trip to a center (Cleveland Clinic, Mayo, John Hopkins, etc.) where there is a great deal more experience with these types of problems. You may need a revision.
Now that's jumping the gun, because dilitation can fix things for many people. However, with your swallowing reflex, they'll have to increase the diameter by a fair amount, if you're just getting a small stream now.
I'm not a doctor, nor do I play one on this forum. I'm just providing some ideas and information I've gleaned through this forum and other sources. My advice (for what it's worth) is confer with others in the medical field who have a great deal of experience with this particular procedure.
Best wishes in finding an answer. We're glad you've joined us, and so sorry to hear about your problem! Hang in there, and try not to panic. There are answers out there. You will find a resolution to this issue.
We're with you!