Underweight concerns

Holly
I found out from my Ob that I'm 10 weeks pregnant and due to my matabolism  I'm naturally 20 pounds underweight.... I've had two miscarriages in the past caused by my weight problem and I'm just worried this one will end the same way... Due to not actually knowing about being pregnant till now I haven't seen an ultrasound or anything yet... So i wanted to know if anyone has ever had a similar problem and to ask for prayers that I make it to term