I struggled to burp when my GERD was at its worst; I burped often but also frequently felt I needed a fizzy drink or something to relieve the sensation of needing to burp. It could be that it's just a sensation rather than actual gas? Do you have gastritis - I think you can get a lot of odd sensations from that.
Have you tried peppermint capsules or peppermint tea? Some say peppermint is bad for GERD but I've always found it helpful to suck or chew mints, tho I can't tolerate tea of any description.
If it's just since you started medication that you've got this particular symptom, then perhaps you need a lower dose or a different drug?
GERD treatment is a long process or trial and error - you'll get there!
New stuff: GERD. Interstitial Cystitis
Lifelong stuff: Food allergies, eczema, asthma