Welcome to HCM,
You are definitely under weight, according to you height weight should be in between 55 to 65 kg before you take any thing first go for proper medical check up by a Physician,to rule out any disorder or hidden disease like TB.
There are some tests like CBC, Urine , Stool test
R&M, FBS,Lipid Profile
, T3, T4, TSH, X ray chest and Ultrasonography
We must rule out mal absorption states.
If every thing is fine then high protein and high calories diet may be planned nutrition supplements and proper exercise and weight training
may be planned to gain weight if it is necessary even anabolic steroids
can be used with consultation of Physician.
Please do not take supplements by your self .
Take good care of yourself.