i'm looking for serious advice.

i'm 15 , 6'4 (i'm not lying i swear ) and very skinny , 62kg to 65kg . i've been trying to get weight for a long time now , i tried healthy diets , different types of food , ones full of protein, fat etc... i even tried eating loads of junk food but nothing seemed to work . last year i had my birthday then decided to try to gain weight and then hit the gym , but i've only lost weight -_- . I felt so frustrated, and people keep pointing out that i'm skinny all the time and it hurts yk . And my parents won't take me to any doctor (i can't take an appointment for myself in my country, i have to be 18) . so i came here to ask for advice from people. i don't know if it's the right community to ask . Any advice? and btw do you think i should start going to the gym after getting weight or now ?