At what stage you should be worried if the kidney stone that has travelled to ur bladder doesn't flush out in 3,4 weeks there is no blockage in urine but burning sensation and mild pain at times?

You should see your primary care physician to rule out an urinary tract infection. Your doctor may suggest an abdominal X-ray or CT to assess the location of your kidney stone.

Depends on size of stone. Stones smaller than !cm generally pass by themselves the 'when' varies. Drink plenty of water and look for it when voiding. Since it passed thru a narrower tube it should pass thru the wider outer tube (urethra) There is a very good chance you will pass it If not passed for 3-4 weeks see your Urologist. Good luck.