Hi Tasha, it sounds a little like gallstones, which can be tricky to nail down. Has the dr done liver function tests & an ultrasound? Also, they should do a hydrogen breath test to check for tummy ulcers. If all of that comes back clear, ask about biliary spasm, which be a bit random but can also be set off by medications like codeine among other (random) things but behaves very much like gallstones. When I was having gallstone attacks they always felt like bad reflux at the start before getting worse.

I also had GERD for a while and found gaviscon to provide the best immediate relief. Longer term the dr might put you onto Zantac or nexium which reduces the amount of acid in your tummy. But if they find any evidence of liver/gallbladder issues, and especially if the attacks have a squeezing or spasm sensation with them, try taking buscopan, it works better than any kind of painkiller for gallbladder attacks.

Hope you get some answers soon