A 2mm stone does not cause sever pain.Most probably,the size is bigger.
It is blocking the ureter
in the lower part and the portion above it is enlarged.
Sometimes,the block will not be relieved and you have to go for a procedure which dissolves the stone.
Get a simple Ultrasound
abdomen which clearly mentions the size of the stone and proceed accordingly with the consultation of your Urologist
Wish you good health