I need help!

Hey girls so I am 16 and only weigh 100.. I am super insecure of my body because I feel like my body makes me ugly, although I have a boyfriend who loves me for me I still feel very insecure and my doctor tells me that I am healthy but do need to gain.. the question is HOW?!? please don’t say to just eat because trust me I do!! is there any shakes or certain foods to help me?!? 😭