Your nausea could be related to your abdominal surgery, definitely. I had my appendix taken out and was nauseous for weeks afterward, and my doctor said that was pretty common after abdominal procedures, just because things had been `disturbed' in that area. The Phenergan and its generic, promethazine, help. Also ginger, in capsule or sucker form, also really helps nausea.

But also, it sounds like you might have developed acid reflux disease. A few years ago my doctors diagnosed it in me, after I had developed extreme nausea, out of the blue, and apparently was very healthy otherwise. I didn't even have other symptoms (not even heartburn). I would go to your doctor and see about this, and if you do have, getting on medication (daily med is needed to control it) like Prilosec, Nexium or Prevacid.
Acid Reflux disease, when not kept under control, can eventually lead to cancer of the esophogus, because of changes the acid causes in the lining. Besides that, if you develop bad symptoms like I did, it will make you miserable.
I have really never had heartburn as a result of it though. Instead my main symptoms are nausea and bad coughing, and even slight trouble breathing at one point. (Acid reflux can cause asthma-like symptoms if it gets bad) This problem can get progressively worse, like it has in me. I've gone from Prilosec, to Nexium, to now Prevacid, as my symptoms gradually became too strong for the first two medications to control.