Weight, weight, weight...am i so concious?

i weigh about 50 kgs.22 years old 1.67 metres tall...i am constantly worried about what i eat...my boyfriend thinks i can eat about anything without gaining weight.i think so too coz i have tried it.but i would like to go back to 45kgs like i was 2 years ago. i havent been eating much or rather at all this wole week and i dont feel hungry.is this okay..maybe il eat next week but m scared the pounds will just pour on and on.