5 wk ultrasound, no sac present

So for those that may not know, I've been experiencing some vaginal bleeding and my doctor sent me for an ultrasound today to try and determine the cause. My HCG level was 209 on Thursday so the tech said we may not see anything until levels hit 1500+. So now we wait to see if my levels continue to rise. It's nerve wracking, but I'm hoping this turns out ok. Has anyone experienced anything similar? I could really use some positive stories!