Are you experiencing any decrease in urine?
Has your doctor said what size the stone is?
Some doctors try to ride it out if the stone is not causing any problems but saying that the stone may get bigger just sitting there also.
Personally I like to get them out as soon as they start bothering me. I've had so many stones I couldn't even give you a number, many I passed on my own, many others I had removed.
If you are not comfortable you should seek to another urologist or sit down and talk to this one ask him why he's not doing anything to get the stone out.
I understand the financial part of it all, it does get very expensive when you have to keep going back so many times.
Did he tell you to strain your urine in the event you do pass the stone and to give to him so he can get analyzed? this will tell you what kind of stone(s) you are making.
Keep us posted..Good luck..