Kidney infection after UTI antibiotic course is done?

I finished my Macrobid antibiotic yesterday for my uti. Now im having pain on my left back side right under my rib cage. So I don't want to jump into conclusions just yet because I don't have medical insurance this month so I'm wondering if anyone thinks it could just be a muscle strain or is it possible to get a kidney infection right after finishing my uti course???

Oh & my pain is very minimal like a 3

It is uncomfortable & no other symptoms....