why am i stuck at 60kg?

hello im 18, 168cm tall and 60kg, i used to weigh 66-67kg (unironically) and i lost it within some months, now im 60kg, i wanna be around 55-57 , it is NOT a crazy unachievable goal, ive BARELY been eating above 1000cal , sometimes i only eat around 500cal for the whole day, and when i go above 1000 its not any higher than like 1300, i work out too i have a gym membership and i go there sometimes, just to feel better about myself and i walk alot! im so mad