Emergency doctors visit has me worried :/

Looking for some insight.. We have been TTC for 4 years after a tubal pregnancy, so finally seeing the positive results has been amazing ! I'm 6 weeks today and woke up with some cramping, which I know can be normal , but given my history I went in to be safe. They found a cyst on my ovary which they said is causing the pain. In my ultrasound they saw the sac in my uterus, which is great news, no tubal this time, but nothing in the sac. The doctor said that's normal this early but wasn't too reassuring, now I'm just feeling so worried. Any advice or similar situations you've been in would be appreciated :)