no baby but sac

I went in a 5 weeks 1 day for ultrasound (due to light brown spotting), which they said it was completely normal. They did a transvaginal ultrasound, and didn't see a baby but they saw a sac. He wants me in again next week (Friday), so one week exactly to see if we can see a baby just yet. Did anyone expierence this and baby appeared and was perfectly fine? My hcg levels are at 3,149 as of yesterday. Don't know if that helps any.