Kidney / side pain after prenatal

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Hello ladies , 
Every time I take my prenatal vitamins I get what I feel like kidney pain that goes to front and some times so painful I go see my dr but all tests (urine& ultrasound) say nothing.  I then decided to stop taking them I really feel huge difference and zero pain, but when I take them again I get that pain so u ended up stopping them for two weeks now . This is my second pregnancy and the same happened with my first!
Has any one went through the same thing!?