Brief Answer:
consult Gastroenterologist/ Orthopedic ( spinal) surgeon.

Detailed Answer:
Hi XXXX,
Thanks for the query under HCM forum.
I understand your concern.
* Pain in the lower left back side of rib cage can be due to various causes.
- gastric ulcer/ GERD/ can present as a burning pain in back.
- Spondylosis / spinal disc problem in thoraco lumber region ,
- kidney infection,
But looking at your symptom of having bloating along with the burning pain, disability to fit on tight waistbands/ disability to walk long when pain is present point towards either spinal problem or digestive problem ( gastritis/ acid peptic disease/ Gerd)
* Investigations- you will need-
- Xray/MRI/CTscan of thoracolumber spine Lateral/ P/A view.
-Blood for CBC/ serum calcium & vitamin D ( to find signs of boney weakness)
- Barium meal Xray/ gastroscopy .
*In this context I would advise you to consult your family physician to start with. He will examine you after getting detailed history of the problem & advise you few investigations to pin point the cause & the will direct you to a
Gastroenterologist / Orthopedic(spinal) surgeon for specific treatment.
*Treatment
Gastritis- It will consist of restriction on certain food ( spicy,oily,food)/ irregular eating habit/ drinking lot of water & bland nourishing food.along with medications to control your symptoms
Spinal problem - physiotherapy, medicines,spinal surgery will be the options.
Please don't worry, consultation of a suitable specialist , proper management & self care would help you out of the present problem.
*self care-Till then
- Have non irritant food , plenty of water/ cold milk when pain is ++/ have regular eating habit/ avoid alcohol/
- avoid lifting weight, forward bending/ turning that instigates the pain. try to sooth the pain with hot/cold compress/ apply local muscle relaxants ( Relaxil ointment for pain, Avoid massage).

I hope, the query has been answered to provide you information as well as guidance Any follow up query is welcome.
Thanks.

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