Thanks for the query.
Looks like the retro peritoneal mass might be obstructing the kidney
and resulting in stones and recurrent infection. Any obstruction to the kidney makes it very susceptible to infections.
You need to see a urologist
and a surgeon ASAP and have the mass evaluated. It could well be a tumour.
While defza may predispose to infections it will certainly not cause the findings mentioned above.
Hope this helps