Confused

Well, everyone... Today I had an ultrasound.  The baby measured in at 6 weeks and sac at 5 weeks.  There was no heartbeat but the doc said at 6 weeks seeing the heartbeat is hit or miss.  I've been spotting brown and bright red on and off for about a week now.  Nothing has even touched my panty liner, I only see it when I wipe.  My cervix is closed.  Next Thursday we are going back for a repeat ultrasound to see if we see the heart beating.  I also have to go for more bloodwork to see what my levels are doing.  I am REALLY hoping our dates were just off and the baby is still growing as planned.  Instead of what happened when I miscarried before.  The ultrasound only showed a sac measuring at 5 weeks, with no baby in it.  Advice or experiences please!!! This is killing me!