5w sac but no baby

I have had some spotting and went to the ER yesterday, they did an ultrasound sound and told me I was about 5 weeks and there was a sac but no baby. My hcg levels were low and dr said more than likely I will miscarry but that in odd cases it’s just too early?? Has anyone ever experienced this before? This is my first pregnancy after trying for 3years.. I’m devastated to say the least.