Weight loss during pregnancy. FTM, nervous!

I am 17 weeks along now. I am 20 pounds down from my prepregnancy weight, and I saw that the fluid volume, baby, placenta, and all is around 8 pounds or so. My baby is measuring almost 2 weeks past the gestational age. Anyways, should I be concerned that I am down 20 pounds (close to 30 when you take the baby's weight and fluid into account)? I looked in the older posts and couldn't find anything that could put my mind to rest.