I was a little "fluffy" before getting pregnant too. My OB was worried that I'd only gained 2lbs after losing like 10 from morning sickness. She told me that as long as my LO was healthy the weight gain or loss is irrelevant, however, no matter how I feel about my body it definitely isn't the time to be purposely dieting.
I have actually eaten more junkfood recently, but in small quantities, than I ever have in life before. I still pretty much inhale veggies though, as well as taking my prenatal vitamins(when I remember =o)