spotting!!

Okay so here's the issue I'm having. lastnight I started spotting brown. after an hour or so it turned dark red. went into er. they did an ultra sound and told me I was measuring at 5 weeks 6 days. and I was supposed to be 6 weeks. not sure if a one day different makes a big deal or not. they did not see a Embryo but they did see a yolk sac which is progress from when I got an ultra sound a 5 week and 2 days. the spotting was back to brown this morning. I'm just very worried. also Iv had my levels taken 3 times all going up wonderfully. last test was at 20,0000.