it's cause your calories are too low and the initial weight loss wasn't actual fat loss. you really need to be eating more. ive been there where i undereat and i lose "weight" quick but after a little while you get stuck since you didn't follow CICO the right way sis it can get dangerous. like first you feel fine with extreme low calorie diets but afterwards the weariness and dizziness will hit you bad
you shoukd recheck your daily protein, carbs and (healthy) fats