Feeling horriable after stoping BC and starting prenatal vitamins

My husband and I have been ttc for 8mths. I stopped BC about 9 months ago and started taking prenatal vitamins. Since doing this I have had horriable nausea and upset stomach (test each month and bfn). I have switched to a prenatal that does not have iron in it and have felt better but wondering if any other women have had same experience coming off bc or starting prenatals ?