Help!!

I got an ultrasound today at 5 weeks, 5 days and they saw the yolk sack in my uterus and said it's too early to see baby but that it's 100% definitely in my uterus.  I had mentioned some right ovary VERY OCCASIONAL MILD cramping, so she checked it out and said there's a 99.9% chance that what she found was the corpus luteum but she wanted me to come back in in a week for another ultrasound to make sure it's not a twin stuck in my right tube.