First let me say I have Acid Reflux Disease and Crohn's Disease so pain between my ribs is a real familiar problem. I also take Nexium, 40mg 2 times a day. My acid reflux is severe. Have you had an Endoscopy to confirm the severity of your Acid Reflux? I ask because you said your doctor gave you a script because you simply asked for it. Rather unusual for a doctor when it comes to something as severe as Acid Reflux can be. Is your doctor a Gastroenterologist? That's who you need to see with this kind of problem.
The over the counter acid test isn't something I would rely on to go off Nexium. Expecially since you experience so much pain when you stop using it. NO. If you are on Nexium the test results would not be accurate because the Nexium is reducing the acid in your stomach. From personal experience, I know that constipation, diet and stress can bring on an acid reflux attack. If food doesn't pass through you like it should, your stomach will make more acid, trying to get rid of the food. Kind of a simple explanation but you know what I mean. Also things like spices, greasy foods, chocolate can bring on an acid attack as well. We're each a little different on just what brings on the pain. Some tolerate things others can't.
It sounds like you need to find a good doctor. Living in a small town means your choice of doctors is more limited. Are there any Gastroenterologists you can see through your insurance from a town close to yours? The travel might be worth it if you can find some answers. I know this is all very hard on you. Don't give up. Keep looking for a doctor that will try to find some answers for you, not just hand you a prescription for yet another medication. But until then, you may want to stay on the Nexium just to keep the pain away.
~~IF WE CAN'T LAUGH, WE CAN'T SURVIVE~~