Recent kidney infection. finished 2 courses antibiotics & all symptoms cleared but pain in both flanks worsened & is severe. no stones on ultrasound.

Get medical help!: If you have bilateral flank pain that is getting worse, you should seek medical care. Of course, the details of when and what you took and for what infection exactly, are unclear to me. Nonetheless, if you have severe and/or worsening symptoms, you should be reevaluated as soon as possible!

Depends.: Certainly any inflammatory process .. even skinning a knee.. doesn't heal up the minute you stop the process (stop the knee rubbing the sidewalk, it still hurts). A kidney infection is pretty severe inflammation. Would often be a week healing aftr infection gone. Can have long term derangement/scarring/cysts after infection. Those and other blockages would mostly have shown on U/S

Flank pain: How was the kidney infection diagnosed? Were you admitted to the hospital? Infection on both sides is very rare and if it happens, one can be very sick. Did you get urine and blood cultures ? What type of abx were you given. In some cases some stones can be missed on a US. A CT scan with kidney stone protocol may be needed. I would see your MD and discuss these issues. Hope this helps.