Was the back pain there when they discharged you form hospital?
If not I would call dr and let them know about it.

Since this has been a long time ongoing thing have you considered a naturopathic doctor?
You could have some underlying food sensitivities that are setting your body up for these recurring infections.
https://duckduckgo.com/?q=naturopathic

Especially if no anatomical or other physical reasons are showing up.