what could be the cause

I'm 20 weeks pregnant and passed out cause of kidney stones. He doctor found some in my urine but never told me what they are made of. My eating habits is great.  I drink over two liters of water a day get my friuts ect. But I stop drinking caffeinated drinks about 3 years ago. Could my prenatal pills caused a change in my body to cause my kidney stones. Its been 4 days and I'm still in pain when will they pass?

[David Rudnick, M.D.]

pregnancy causes changes in body chemistry that can lead to stones.  You would need to do a urine chemistry test after your pregnancy ends to find if you are at increased risk for stones going forward. Prenatal vitamins are unlikely to cause stones, and are of critical importance to a healthy pregnancy.