Hi In Currently 17vyears Olf Turning 18 In A Month

Hi in currently 17vyears olf turning 18 in a month but i was worried about a problem that is currently ongoing and affecting my health. In the past 4 months i have rapidly lost 5.2 kgs and the worst thing about it, is that i was already underweight. Im currently 6'0 at 63.5 kgs and seeking on ways to rapidly gain weight either through nutrituonal considerations, which have not been of great use, or prescription drugs/medicine.