Do i have gerd? i feel a pressure on my throat and/or chest, slight nausea, and lots of burping. medication (omeprazole and gaviscon) has been useless; diet changes have made no effect; and posture does not affect symptoms at all?

There are several reasons for you condition. You should see a doctor to evaluate you. I am thinking of the esophagus and heart as areas of concern. I would consider Eosinophilic Esophagitis, gastroparesis, Gerd,

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. If you are overweight, losing weight is imperative. It would be prudent to see a doctor, preferably a GI doctor. Wish you good health!