Fluctuating hcg levels?

Back on 12/29 I went to the ER because I was bleeding. I was about six weeks and some days. They did an ultrasound and said that there is nothing in my tubes or my uterus, and that my levels were 84. I passed tissue on 01/01 and then did more bloodwork the following day and my levels were at 74. I went to the doctor on 01/15 because my light bleeding got really heavy and read again, they did an ultrasound and said that there is nothing there, but this time my levels were 204. They are having me come back in for another ultrasound to make sure it’s not ectopic. I know fluctuating levels is a very common sign of an ectopic pregnancy, but I would be 10 weeks by now. Wouldn’t they have seen it on the last ultrasound on 01/15? They said they checked my tubes and didn’t see anything. I know no one on this app is a doctor, but I am so confused at this point and would like to know if anybody had a similar experience. This is suspense until my appointment tomorrow is killing me. I really want to stop bleeding and be able to heal, but I feel like nobody has answers for me