Slow rising hcg

Hannah

2 days ago it was 2900 now it’s 3900, I’m supposed to be a little over 7 weeks according to lmp . Ultrasound just shows a growing sac. Dr said either get Cytotec or come back in another week for ultrasound. What would you do? I’ve had 3 or 4 ultrasounds already that show nothing but a sac.