After my Nissen Fundoplication, I also would have some embarrassing nasal backup issues, but only if I hurried my consumption of food and drink. Certainly, totally avoid any carbonated drinks or high fat foods, and stick with a very soft diet would be my suggestion. Also, keep in mind that your esophagus is swollen from the surgery. It will soon repair itself, but cold fluids, taken slowly, will help.
I don't know about what is causing your nasal voice. I was born with one! Keep us informed.
I am hoping u get a reply from a member that has had this surgery...but 2 weeks may be rushing it wanting to get back to certain things, all of us are different as to how long our body takes to get back to "normal" what ever that is....
Try to be patient....and when u see ur Dr for post op visit ask about this issue with ur voice....
Wishing u a smooth recovery.