About the only way you are going to find out is to get this nuclear test done, a stomach emptying test, and I hope you have insurance!
I was misdiagnosed with gastroparesis, and they put me on Motilium, but I didn't get any better, so they did this nuclear test and that's not what I had. What I have is a type of GERD that only happens in the upper part of the esophagus, and can wreak havoc and the symptoms are pretty much the same. Also, check into IBS.
You are not alone, trust me. I have the same problem, and every symptom of gastroparesis. I went to gastrointestinal specialist, who told me it could be multiple things (acid reflux, a gluten allergy, etc) but wanted me to have an upper endoscopy done, which I cannot afford. I've done some experimenting on my own with some of the information various doctors I've seen have told me. What I've theorized is that I have a stomach emptying problem (a possibility that the gastro specialist told me), in which my stomach empties at a slower rate. My particular problem was occurring in the mornings; I would wake up and know that I was going to be sick, not by a nauseated feeling, but because of the "rotten egg burps". What I've figured is that since my stomach was not emptying the right way, the food I'd ingested in the hours before I fell asleep was sitting in my stomach all night and had essentially rotted. The only way I was figuring to relieve them is to vomit the food up, and then I'd feel fine and the burps were gone. So based on something a technician who ran a CAT scan on me last year to help figure out this problem told me, that your stomach empties on the right side, and so if I wanted to lay down (after drinking the contrast solution before the test) that I needed to lay on my right side. I've started doing that at night if I've eaten in the four hours or so before bed. If I wake up in the middle of the night and feel kind of hungry, I know my stomach emptied correctly and I can roll over another way that's more comfortable. But sleeping on my right side at night has drastically reduced the amount of times I get the rotten egg burps (it used to be like every other weekend, when I'd eat later at night and sleep less; now it may happen once every other month) and when I do get them I just induce vomiting until everything comes up and I see just stomach acid, and then I feel fine. I know the last part doesn't sound fun, but going all day with the taste of rotten eggs in your mouth is less appealing to me than thirty minutes of nausea. Hope this helps, at least to know that you aren't alone.