A 4 mm wide and 8 mm long kidney stone is too big to be passed as such in the urine. Drink plenty of water and talk to your nephrologist regarding the treatment of kidney stones which include pain killers, trying avoiding taking calcium rich foods. If the symptoms persist then surgical intervention is needed. This includes, ureteroscopy, ureteral stent placement, ESWL and percutaneous nephrostomy.
I suggest you to get an evaluation done from a urologist and discuss the various treatment options.
Hope it helps. Take care and regards.