So confused..

According to the beginning of my last period, I should be 6 weeks 4 days. I'm too anxious so I had an ultrasound yesterday. I have a huge cyst on my ovary and a nice patch of thickened endometrium, but cant see a baby or a heart. Had my blood done yesterday and my hcg is 437... Which is roughly 4 weeks. The timing is so off. The only dates we could have conceived are April 25, or May 23, but that would make me like 18 days pregnant. I go in tomorrow to have my levels done again and I'm pretty nervous. Anyone had something similar happen?