What is with my body

Hi guys

I got a Problem and a question.Atm i am at the Limit of underweight.

I am with 121 lbs at a 5′6.54 feet.I am not eating that much bc of my eating disorder; but atm i am in recovery.Bc of head and body i just get the 500-600 calories per day; but sometimes i am not Sure about my body.There r days it really looks fat; mostly on my knees.Is it possible that there is more fat on my knees bc i am not eating enough? I really am a sporty guy. I do sports most Times of the week and i love to be outside and walk a lot ( sometimes i get my 20.000 steps on a day).So why i got this much feet on my knees?And atm i am in the week before my period. Is this here normal too to have more fat or “Look fatter” before my period? I know its normal to Look bloated on my stomach, but not gaining fat on my knees. And thats before period. Or is this water before my period or bc of my anorexia ? I dont know anymore

Thanks for support