Hello Sir. I Am 25yrs Old But My Weight Is

Hello sir. I am 25yrs old but my weight is just 30kgs. This makes me feel less confident and inferior. I want to gain weight but I don't feel hungry. If I try to eat anything I feel pukish and sometimes I even puke. I would like to tell you that few months back I had taken some weight gaining tablets. I don't know the name but when I take that I can eat but when I don't, I don't feel like eating. Please help.