I have posted a lot fairly recently about my 15 year-old daughers' Gis problems.My suggestion is to try to find out the cause, and not just treat symptoms.
Some treaments that are good for one thing, can hurt something else. For instance, zantac or prilosec can worsen overgrowths of baceria or yeast.
Has she had an endoscopy? If she does have one, make sure they biopsy for bacteria or yeast. Also, alternative GI doctors can do a lot of testing to find out what is going on.
My daughter's story is very long, and it has taken 18 months to figure things out, mainly because "mainstream" doctors had nothing to offer other than pills like Prilosec.
Kids who have been on Lyme meds are a special subset of patients that don't fit the formulaic picture most GI doctors go by. Believe me, before this I was quite conservative, but this experience has opened my eyes.
Even with a biopsy (and photos from endoscopy) that showed huge amounts of yeast, the GI doctor only prescribed two weeks of 100mg Diflucan and said she could eat anything.
As it turns out, she has needed much more Diflucan, and has to restrict her foods severely.
The Diflucan alone got rid of the burning sensations and GERD. But there were other systemic and gut problems to deal with.
If yeast is a problem, it often causes "leaky gut," also known a intestinal permeability- because it sinks roots in the lining and causes it to be porous. Foods and toxins migrate through the now permeable gut lining directly into the bloodstream, causing all kinds of problems that resemble food allergies.
For my daughter, this first caused stomach pain, nausea and diahhrea. Then she started having dizziness, weakness and other stuff. Finally, her capillaries became leaky from inflammation and she swelled up with more than 20 pounds of extra fluid collecting throughout her body.
The interaction between the yeast, gut lining and certain foods also causes a lot of inflammation of the gut lining, which causes pain and diahhrea.
So far, she has done the Diflucan, takes probiotics and Similase (enzymes) and is on an elimination diet. Avoiding dairy, gluten, corn, soy, sugar, citrus, eggs etc. has greatly helped her pain.
We are trying adding back foods one at a time to see if they cause problems. The first one, milk, was a disaster and has caused pain, nausea and diahhrea for two weeks now! She only had milk one day, 4 times, two weeks ago.
For more than a year, she was eating ice cream to soothe her stomach, and it was probably causing the symptoms she was trying to alleviate!
Your daughter's problems may be very different. The important point is to find out as best as you can what the cause is, because treatment choices should depend on this.
And, any MD involved should recognize that Lyme patients, who have been on antibiotics and other meds for a long time, pose special problems and can't be treated in a cookbook fashion.
One other thing: stomach acid serves a lot of purposes: digestion, obviously, but also acids keep things in balance in the gut, and prevent overgrowths (as I siad before). Meds that reduce or eliminate or counterct acids may have effects if used long-term.