Welcome to Healing Well! I'm sorry to hear you're suffering! It sounds like you're on the right track, and if you're also an asthma sufferer, you'd best take these symptoms seriously. I also have asthma, and like you, when reflux has been a problem, my lungs have suffered.
The pain in your back sounds a lot like gallbladder problems, although I'm sure some experience that pain with reflux (I never did). With gallbladder issues, bile reflux can be a problem as well...it's also very sour tasting, like acid.
Can you get in to see a GI doctor so you can be diagnosed? I think that would be a very good idea.
Of course your diet will hugely effect any GI problem you are having. If you search "GERD triggers" (and perhaps even "gallbladder triggers", although at your age, it's not as common, but certainly not unheard of) you can learn about ways to avoid some of the problems you're suffering from.
As I said, you can get into serious trouble with asthma and reflux. Over time, as my GERD worsened, my lungs got dangerously involved, and I was on lots of medications to keep me breathing. Some who suffer from extreme reflux for years get permanent damage to their lungs. Just keep in mind that if you're getting lung symptoms, you need to take them seriously.
Two years ago I had GERD surgery because of my severe asthma symptoms. Thankfully it worked, and my lungs are much, much better.
I'm glad you've joined us! Good luck with finding answers to your problem!
I'm sure others will be by to share their own experience and support!