Am I having another MC ?just found out this week

Yasemin • Married to wonderful hubby! Have two gorgeous girls 16 and 9. Trying for number 3.
Tuesday I tested positive. Yesterday had my hcg done and found out the number is 669 I'm supposed to be 5 wks 3 days today. The number seems very low for 5 wks. I'm going again tomorrow to see if the numbers double. I'm not having any mc symptoms yet other than slight back ache when I'm on my feet too long. Anyone else have numbers this low. I'm so bummed as I've been through a lot the past three years trying to have a baby. Keep me in your prayers, please!