Had slight cramping and brown spotting

I had an ultrasound last Friday all they seen was the gestational sac and maybe a yok sac but she wasn't sure. Today I had slight cramping and brown spotting only seen it when I whipped! So went to the ER had another ultrasound not much change in the four days since my last one they couldn't see a yok sac either. Has anyone went through this before??? I go Thursday to meet with my ob and she what she has to say and I have another ultrasound scheduled May 21