What Causes Left Sided Flank Pain When Suffering From UTI And Bladder Infection?

I have had left flank (? - mid back on left side Sometimes extending to left side,) for the last week. I have been on Keflex 500mgm 4 x/day for 10 days, ending yesterday but have been on antibiotics repeatedly in the last 3 months for UTI. I am now to take one 500mgm dose daily. I had a CT scan 2 weeks ago. I thought it included kidneys. I had a bladder scope 2 days later. These showed only bladder infection. Should I be concerned of kidney involvement. I have no fever. Heat has not offered any help. I have difficulty sleeping due to discomfort.