Low HcG levels

Today I am 6 weeks along. I got a call from my midwife yesterday telling me that my last HcG test came back lower than they had expected. I have had 2 miscarriages in the past and am trying to stay positive but also freaking out a little. We tested my HcG on Thursday and again on Saturday. She said they expect to see those numbers double and mine were not quiet there. She wants me to schedule another one for Tuesday and a Viability Ultrasound for next week. Has anyone else had this happen or been through this? I am too afraid to google what a lower than expected HcG could mean. Dr.Google never helps. I’d love to hear from anyone that has gone through this too.😰