Hello and hope you are doing well.
Small stones are let to pass naturally, with medications support and by drinking plenty of oral fluids. Only if it does not pass then other options like Extracorporeal shock wave lithotripsy (ESWL) are used to break up the stone. So, follow the instructions given and follow up with your doctor to see if the stone has passed.
Hope this helped and do keep us posted.
I was born with a condition that causes my body to create kidney stones. I have been to the emergency room 4 or 5 times in the past 18 years for the large stones, small ones pass ok. My first stone caused bleeding and severe back pain also with pain in the lower abdomen area along with hot/cold flashes and vomiting. It may feel like someone is squeezing your kidney while at the same time stabbing it with an ice pick. I first though it was my appendix. I was wrong.
If you are in any serious pain your doctor should send your info to a urologist that can help you but I think you should be able to pass it with little discomfort. Water, water, water. I have to drink plenty of water every day. This helps to flush it out and to keep the kidney tissue from squeezing the stone. Drink enough water to make the urine light yellow to almost clear. Stay away from soft drinks if you can help it and processed foods high in sodium.
I currently have a large one in each kidney right now around 7mm-8mm in size which may require the doctor to blast with ultrasound.
This link may be of some help to you- http://en.wikipedia.org/wiki/Kidney_stone.
3mm should pass through just fine as I have passed at least a dozen small stones over the years. Products with citric acid, mainly lemons will help prevent new one from forming although it will not help any current ones.Good luck.