My ultrasound confused me...

So with my irregular periods and the fact that I was on birth control no one knows when I conceived not even myself. so my doctor wanted to start doing ultrasounds early... based off my lmp I'm only about 3 weeks and a day. but with todays ultrasound, we only saw a black speck and thickening of the uterine lining. aren't I suppose to have at least a sac by now?ugh the anticipation is killing me! but anyways... they also took my blood so we will see if my levels have doubled tomorrow 🤔