Hi and welcome to HCM!
Thanks for posting your query here.
The reason for hydronephrosis
of kidney is obstruction to the urine outflow in the urinary tract- from renal pelvis
to ureter to urinary bladder
to urethra and to out. Any obstruction in the pathway will result in accumulation of urine in the back flow and results in swelling of the kidney. The acute pain on the left side 2-3 weeks could be of renal stone which would have passed out in the urine. For this reason I think your doctor has advised you for an X-ray KUB.
Please check the renal parameters which will give you a clue. The swelling of the kidney will get reduces slowly if there is no other pathology.
For the gas or acidic problem you can use omeprazole
one tablet daily untill the symptoms resolve.
Hope this is helpful to you.