Low hcg levels at 5 weeks pregnant

Hi ladies, I am supposedly 5 weeks and 4 days pregnant. I have had 4 positive pregnancy tests and a blood test to measure hcg levels. My levels are at 399. The doctor said this is low and chances are the pregnancy won't be viable :( I have a repeat blood test on Friday to see if my hcg level has increased. My LMP was September 26th, I am almost sure I ovulated on October 17th. Is there a chance of my pregnancy progressing even if my hcg is only at 399? I saw that for five weeks pregnant hcg between 18 and 1786 is classed as normal. So I'm really confused. Please can someone help me, let me know if you had the same experience ect. Thanks