I'm so sorry! I never knew Fifth's Disease was something to be concerned about until a couple days ago, when I read a CDC informational booklet that my midwife gave me. It was pretty unspecific, just said that it could be a cause for concern, but it did say, to paraphrase, "Fifth's Disease has few symptoms in children, so assume all young children have it and try to avoid them all", which I thought was pretty unhelpful information, and more than a little strange.
I have a toddler and I know that Fifth's Disease is so common. I hope you and your baby come through this easily and without too much worry!