My doctor said my baby was measuring small when they did the ultrasound...?

I found out last Friday that I am 5 wks pregnant. I had some concerns (long story) so I went to my OB/GYN to make sure everything was going well. She did an ultrasound and said the baby is measuring very small for how far along that I am. She said that even though it is very early in my pregnancy, the baby should be bigger than this. They could barely see anything on the screen...she had to dig to find it. She even checked for ectopic pregnancy. She ordered bloodwork for me to have yesterday to check my hormone levels and for me to go back tomorrow to see if the hormone levels have doubled. Has this happened to anyone else? What was the outcome? Please be honest. Thanks.