It can really much better identify some potential causes versus via blood work.
Once you have some answers, sometimes you can help prevent stones by change of diet.
C~
My suggestion would be to do the test as the Doctor requested you do, nasty or not in your opinion. You had you first stone at 15 and now you're 22. You've got a lot of life ahead of you and probably the Doctor is trying to gain some info so she can advise you regarding what you can do you either cut down on, or avoid getting more stones and more frequent stones.
I'm not kidding either, because at 22 you want all the info you can get to avoid these painful things in the future. Once you get a stone, like you did at 15, you're much more prone to getting them again and again, and as I said, you have a lot of life in front of you. I didn't get my first stone until I was in my 40's and as of now, I'm 68 and I stopped counting at 30 stones several years ago.
Good Luck and please let the doctor help you any way she can.