I had my first kidney stone last summer followed by 3 more in the span of one month. It started with excruiating pain in my upper groin area and I rushed to the Emergency Hospital where it was diagnosed as 1 stone. They did not do an ultrasound but rather gave me pain killers in the ER such as morphine which they cannot prescribe of course. I was there for hours and then released like you with Vicodin, which I decided not to take, and just bear out the pain. I was also scheduled for an appointment with a urologist to bring the stone(s) in once passed with through urination.
Now, here is an explanation of what you are likely experiencing as the stone grains are being caught in the strainer. When they broke up the stone, it is not down to the size of grains, but rather smaller stones. My first one was the size of a kernel of corn and others got as large as a good size rat dropping. The pain you are feeling is because the stones are stuck in the ureter, which is a very small tube between the kidney and the bladder. Once the stone(s) move out of the ureter and into the bladder, you won't feel the pain anymore. It took me a few days for the pain to let up. Once the stones are in the bladder, they will ultimately pass with your urine. It will not be painful. They will just pop out.
As to the cause of the stones, when they are examined, your urologist will explain the type of stone(s) it was. There are three types. The first is calcium oxalate stones. These are caused by high-calcium foods (diary products) and calcium or vitamin C supplements. Limit high-oxalate foods (such as cola, tea, chocalate and peanuts. The color of the stone is black. The second type, which I have, is uric acid stones. These are caused by high purine foods such as anchovies, poulty, and organ meats. These foods increase uric acid production. I am now on medication (Urocit-K) three times a day and haven't had another stone since on the medication. The color of the stone is brown/yellow. The third type is cystine stones. These are caused by high-methionine foods (fish is the most common) These foods increase your production of cystine. Since my diet consists almost exclusively of poultry and salmon, my stones may have had a little of this as well. I am not sure the color of these type of stones.
I hope this provides you with some helpful information although doesn't eliminate the current pain. Only time will do that as they pass. For those who have never had kidney stones, the medical profession likens the pain to be as severe as when a woman gives birth.