My Obgyn Can't find the baby on the ultrasound

I was in a car accident and I found out I was pregnant and they estimated I was 4-5 weeks and that was on November 13th it's now December 9th and I came in for my appointment which would have put me at 8 weeks and a half or 7 weeks and a half I went in for the ultrasound and my doctor couldn't find the baby only the sac she says it might be because I'm too early but I feel like I'm further along I go in next monday. I've been having sharp back pain but no bleeding. I really hope I haven't miscarried I feel less and less symptoms and I'm getting worried please pray for me I really want my baby so badly.