Low levels? Help please

Ok so I have posted a few tests over the last week. I had 2 positives last week. Then a negative yesterday morning and a faint line at night. Came to er to get checked. They said my hcg is 22. So I'm either newly pregnant or miscarrying. I had a period one week before my positive test. And that period was 16 days late. I took a test with FMU the day before that period started and it was negative. They also did an ultrasound and there was nothing. Has anyone had any experience with anything like this?