My dr has me worried...

She says she "may" see a yolk sac but can't tell, and I'll have to come back in two weeks for another ultrasound. She said she's unsure if it's going to be viable or not, and that I need to avoid strenuous activity until then.. I'm 5 weeks 5 days. 😔 anyone have ultrasounds that looked like this that ended up fine? I have no history of miscarriages, and have one healthy daughter. And I feel like I definitely see something in there! I just don't understand why she'd even say that!