First ultrasound

The only thing that was seen was an empty sac, she didn’t measure it so I have no idea how big it is. the lady said it’s to early to confirm what it is, she said it’s a cyst filled with fluid and I have to go back in 2 weeks time. She didn’t really say a lot else. According to my first day of last period I’m 7 weeks today, But my periods are irregular. Also I probably wouldn’t have conceived until end of December. Is this normal to see as this time in the pregnancy?