Chills, sore back after resolved UTI symptoms

[redpandamonium]

Was on a 3-day course of Bactrim for a UTI with all my usual symptoms (burning, pressure, nausea, fatigue, malaise). I took my last dose on Saturday night. Though I thought I had a return of urinary symptoms (burning) on Sunday night, by Monday everything had resolved. Today  I started getting a sore back though it is unclear to me whether it is muscular. It is almost reminiscent of the onset of a case of pneumonia I had 5 years ago. Tonight I started getting chills, which lasted for about an hour with no fever, and while those have stopped for the moment, my back is continuing to feel sore (in the middle, just under where my bra strap crosses). It does not hurt to move. Gently rubbing my back makes me feel better in that moment.

I do not have a fever.

My thoughts in order of concern/likelihood:
- Concern for a kidney infection, though I still do not have any other urinary symptoms
- I have been moving a lot more than usual today which might have just have made my back muscles sore
- I have been constipated and took some polyethylene glycol a couple days ago; sometimes digestive issues can give me the chills and make my back sore, though usually it's my lower back
- pneumonia?