3 days late, cramping but negative tests??

Hey guys! My husband and I started trying to conceive this last month or so. I've never been on birth control so I've always had periods right on schedule. Never late. Today makes me 3 days late. I'm cramping like I normally would be but pregnancy tests say negative. Is it possible I'm preggo? I started taking prenatal vitamins too last month and have heard they can mess with your cycle??