Since these symptoms have been going on for quite some time, it would be helpful to make an appointment to see your doctor
for more advice. I would recommend that you see either your primary care doctor
or your gastroenterologist
It sounds like you have been well treated for acid reflux problems, with both the Nissen fundoplication procedure and also with your continued use of an anti acid medication (Dexelant). I highly doubt that your continued issues with gas are related to your acid reflux issues, so this would be another reason to have a recheck with your doctor.
Gas is often caused by certain foods. It can be difficult to figure out which foods are the culprits however, and it might be helpful to use a meticulous food diary, with the help of your doctor. Additionally, eating small meals and making sure to chew your food very slowly can keep you from swallowing air, which makes the problem of gas worse. Avoiding carbonated beverage and chewing gum can also be very helpful.
Make an appointment with your doctor as soon as possible. In addition to evaluating this causes of gas, they can also look for other medical problems which might be the cause, such as intestinal infections and irritable bowel syndrome.