weight changes?

i have been very careful to put in my foods and their ammounts but i am confused by the -250 to -750 to lose a specific amount of weight. I am over weight but not terribly and i am trying to eat between 1200 and 1400 calories a day, never going below the recommended 1200, but some days i just cant get them all in! i know that sounds crazy, but i have changed the foods i am eating and i am soooo much more full off so many less calories that some days i struggles to make 1000. could i be doing something wrong? I am weighting my foods and measuring them out to be sure my servings are correct.
I know that i havent been dieting and exercising very long, and that i shouldnt be seeing drastic results by any means, but i dont want to hurt my body....so should i be concerned that i am usually really over in the -?