Information provided by patient.  After second COVID vaccine dose on 2/1 at 10:20am, I woke up around 3am on 2/2 with chills and shaking. These chills alternated with sweats - waking up frequently either with chills or sweats. These symptoms ended around 1900 on 2/2.  Also on 2/2, I began getting left flank pain. I thought this was muscular. Throughout 2/2 and 2/3, the flank pain became worse and worse and I realized it may be a kidney stone (I have had a kidney stone before). I left my work shift early on 2/3 to go to the ER at 2100. There, it was a little complicated because I am pregnant and could not receive a CT scan to check for stones. Based on the information gained from ultrasounds and the UA, they decided to treat for pyelonephritis. I left the ER around 0130 on 2/4 and picked up pain medications and 14 days of cefdinir.   I do know this may not be related to the vaccine, but I think we need to report everything in case there are trends.  ER Provider notes as follows: 31 y.o. female who arrived by Home presented to the emergency department for left flank pain that radiates to her left groin. The pain has been present since yesterday and it is sharp in nature. She took tylenol at 7pm this evening, but it did not help with the pain. She is also 12 weeks pregnant. Patient reports that she passed a kidney stone 3.5 years ago. At the time, she was told that she had an additional stone in the left kidney and has been following with urology. She also reports nausea that has improved with Zofran. Denies fever or chills, urinary urgency or frequency, or blood in her urine. Patient had an ultrasound at Hospital two or three weeks ago that showed a viable IUP. This is her third pregnancy. She denies complications with previous pregnancies and reports two prior cesarean sections.  Patient is sitting up in bed, in no acute distress. Vital signs are normal. Patient presents for left flank pain for the past day that radiates into her groin with associated nausea, and she is 12 weeks pregnant. She has a history of a kidney stone three and a half years ago with an additional stone present in the left kidney at the time of diagnosis. Will obtain CBC, CMP, UA, urine culture, POC kidney ultrasound. Given 1L IV NS bolus, IV zofran and IV morphine.   DDx:  Nephrolithiasis versus UTI versus pyelonephritis versus ovarian cyst versus musculoskeletal etiology   On reassessment, UA negative for nitrites and leukocyte esterase but positive for 50-250 bacteria perr hpf. POC kidney ultrasound negative for hydronephrosis and UA negative for blood. POC US showed IUP with FHR in 170s with good fetal movement. POC renal US repeated after 1L IVF without evidence of hydronephrosis. Will treat for asymptomatic bacteriuria in pregnancy with cefdenir for 14 days given concern for early pyelonephritis. Nephrolithiasis is still possible but unlikely cause of symptoms as there is no sign of obstructive uropathy on bedside US. Through shared decision making, will not undergo CT limited high for stone evaluation at this time given risk of radiation to fetus. Will discharge home with plan to follow-up with OB and PCP in 1-2 days - also provided Rx for roxicodone and miralax. Strict return precautions discussed. Patient voices understanding and agreement with plan. Denies further questions at this time.