I Developed Severe Low Back Ache On The Left Side

i developed severe low back ache on the left side about two weeks back..apart from MRI i also underwent ultra sound. this latter test revealed right kidney measuring 10.62 cms and left kidney measuring 10.13 cms. calculus of 6.6 mm observed in left kidney..
important observations as follows..
. right hydronephrosis
. left renal calculus
. grade ii prostatomegaly with significant post void residue..
base on above i have been advised to undergo slice CT scan..
request as to know is it very alarming and what is normally the management in such cases.