Hello everyone. Here's the situation: my first day of last period was …

Hello everyone. Here's the situation: my first day of last period was March 24th, on the 11th day of delay all tests started showing //, I took a hCG test and it came back at 36.9. The doctor says there is a pregnancy, today I had an ultrasound and they found nothing, the test today showed pregnant 2-3. Tomorrow I will have another HCG test. Have you ever experienced something similar? I am very worried and want this baby.