I was 45KG at 160cm so I know exactly what you are feeling. I can’t tell you exactly what to do as I don’t know how your body personally works (dietary intake, exercise regime, medical) and I am not qualified yet.
I do recommend you see a qualified personal trainer to give you some tips. I personally started eating a few more carbs during the day such as wholegrain breads, beans, pastas & I also increased my protein intake ALOT, I cut back on doing cardio everyday, down to 3 times a week & started lifting weights to build muscle so I stayed small but I started looking healthier instead of skin & bone. :) x
I find hiit training works best for me, I can still maintain muscle in my legs but I also shed the fat so they stay lean instead of muscular.
I don’t have a specific training program, I constantly change my workout routines. I do a lot of HIIT training though & i also incorporate weight training 1-2 times a week.