Low HCG levels rising slowly- Is pregnancy still viable?

hoping12345

My fertility doctor says my pregnancy is 100% not viable based on hcg beta tests and suggests I stop taking progesterone (100 mg twice daily). I am 42 years old. I am 5 weeks and 4 days pregnant and am not bleeding or cramping. Do you consider based on the HCG numbers below that the pregnancy is not viable? Should I continue with taking the progesterone? If I stop, I will likely miscarry.

-4 weeks and 1 day at 163

-4 weeks and 3 days at 310

-4 weeks and 5 days at 482

-5 weeks and 1 day at 831 -5 weeks and 4 days at 887 (today)

*****Update****

 Hi, thanks for all your comments.  I wanted to update this and let you know that three days later, I went for a second ultrasound and blood work from another doctor. They still found an empty sac and the HCG rose to 1060, no viable pregnancy. Thanks again for all your support.