Miscarriage or what?

I randomly started spotting brown like discharge last night but no cramps or discomfort, nothing concerning until hours later where it then got heavier and brighter. I went to the ER and they did a ultasound and urine test which confirmed the pregnancy but they couldn’t find anything, no sac or anything and stated that my pregnancy levels are low. They said me bleeding could either be a early sign of pregnancy, pregnancy in the wrong place or a miscarriage. The app says I’m 6 weeks and 1 day. I don’t know how to feel about this or what to think. They said hopefully over the weeks my levels will increase. Has anyone ever had a full pregnancy but bled?