Why am i so skiny

Ive been too skinny all my life, underweight.
I eat enough and never had any problems eating quite the opposite even especially as a teen I had enormous appetite tho due to anxiety I only ate at home because couldnt have people watching me eat and felt ill seeing others eat but still I ate plenty at home so all meals except lunch and still skinny. Ive been accused of anorexia, been accused of bulimia and its really offensive and rude not to mention who even asks such an insensitive question about such a sensitive topic such as another persons mental health and on top of that expect them to be like "oh yeah I totally do!" like its a fun simple thing to share with people.
I dont like being skinny for that reason and for the reason clothes generally fit better when you have some curves, in my opinion. I dont know why I am not able to gain weight its just impossible and I guess I will gget advice like eat specific health foods etc that I cant afford at this point in my life. I feel like I should gain anyway I mean everybody else does. If I see a video of myself its awful because my spine is visible and the bone sticks out below my hands like my wrists look like you can snap them just like that it cant be good I think and I know sometimes my weight changes because a few years ago I weighed 45kg which is little but the most ive ever weighed but soon it was back to 40kg and as a teen I used to weight 37-38kg. I dont know why no doctor ever wanted to investigate it