IMO, taking a multivitamin doesn’t break a fast. However, make sure that the multivitamin contains enough of the minerals you need. Are you three days in on WATER ONLY?!?!? If not and you ARE taking a multivitamin, I’m still shocked if that’s all you’re taking while on an extended water fast. If I don’t add magnesium and salt to my water and take extra potassium, I’m sick as a dog. Also, I’m pretty sure if I took a multivitamin on this empty stomach, it would make me feel sick too.