Overweight and pregnancy!

I am about 50 lbs overweight. I used to be a good decent size before my son was born, but had a pregnancy related thyroid disease that caused depression, anxiety, and weight gain. It has been 3 years now, and I really have had a difficult time getting any weight off. I'm really wanting another baby, but I'm terrified of adding more weight to my body. Can a person get for during pregnancy?