When your cat scan was done, was it read by a radiologist and then given to your Urologist or ER doctor? It should have been as that is the normal procedure. Your Urologist or ER doc should have told you what you should be doing, etc. In case someone missed a beat and you weren't told anything, a 3mm stone can cause you a lot of pain, as most stones can, but can usually pass on its own without the definite need for surgery to remove it. I'd be drinking water and then drink more water and then more again.. The water will help it pass and help flush it out, so drink as much as you can handle. If you have been given a prescription for Flomax, get it filled and take it too. That will help the stone to pass also. If they gave you a prescription for pain killers, get that filled and if the pain is severe enough, that should help you to some degree with your pain, depending on what pain killer you have. The pain from a stone can get intolerable for some sufferers, and when that happens you may have to return to the ER for a shot of a stronger pain killer. It is hard for me to say from here and it all depends on your pain tolerance level and a few other factors.