Im so confused???

So I got BFP on April 20th. But I have been bleeding consistently for almost 2 weeks now. So I went to the ER thinking that something is either seriously wrong or I was having a miscarriage. They ran a bunch of tests and did an ultrasound. My hcg was 80, I was positive for a UTI and they estimated I was 4/5 weeks along, but they saw no baby/sac on the ultra sound. Even with the bleeding, back pain, cramping, nausea, they still told me that everything could be fine. How is this possible?? What should I expect here, I am so confused and I just don’t understand. They couldn’t answer anything and just told me to follow up with my OB/GYN. So I’m calling to make an appointment tomorrow.

If any of you have any experiences like this I’d appreciate anything you could tell me. I was pregnant with twins and lost one of them very early on and went on with a regular healthy pregnancy so I’ve never had anything like this in regards to loss.