Stopped taking Prenatal Vitamins...

Meredith
My husband and I have been trying to conceive for 6 months. I know 6 months is not a long time... but I've seen enough negative pregnancy tests to put me in a slump. I stopped taking Prenatal Vitamins because I have half given up. This seems stupid to say, but taking them reminded me of our failure. My question is, what if by some crazy chance we got pregnant while I am no longer taking them? How harmful is it to our baby to not have been taking them? Can I start taking them when I find out I am pregnant or is that too late?