Breast feeding !

I've been nursing my son going on 13 months ! I can't keep weight on , infact I only loose it ! I weigh 102 . I'm exactly 5 foot ! I was tiny before I got pregnant but i stayed at a steady weight . My weight keeps fluctuating , and I'm really beyond irritated with it ! I eat healthy , and I eat a lot for the extra calories . Would BF , cause me to have a hard time keeping on weight! ?