Pregnancy questions

I went in for a blood test bc i was 3 weeks late, and the doctor said the test showed I was pregnant but my levels are really really low. He set up an appointment for in 5 days, he said if my levels aren’t increasing, that’s not a good sign. I was kinda in shock from him saying I was pregnant to wrap my head around the rest. Any ideas or personal experience on what to expect if my levels aren’t increasing?? Does it mean I’m going to have a miscarriage or have already had one, I was spotting some yesterday and it got a little heavier today.