Gaining weight fast. Feeling down.

Natalie • 2 losses and 1 beautiful daughter. Pregnant with #2 and praying to make it all the way.
I am gaining weight so fast this pregnancy! I am 17 weeks tomorrow and gained 12lbs. I am 15lbs way from my final weight with baby #1. Not even half way through pregnancy and gained nearly half the weight. 
Is this normal for baby #2?? Worried I am going to gain 50lbs!