Looking for some input :)

1st pregnancy!I have been having A small amount of Brown discharge for about 10 days, only one night was it a little red, never enough to wear a pad or anything. Got an ultrasound at 5w2d and they didn't see anything, clear blue still says I'm 4-5 weeks along and I've had no pain or anything but Doctor thinks I'll miscarriage or already have since there was nothing and I have the brown spotting? Ordered blood work so i go again tomorrow but I'm getting so impatient! Ive read mixed things online-is that early enough where they might have missed it? Or do you typically see something that at 5w2d?