How do I stop looking so scrawny???!

How do I stop looking so scrawny???

I am 5"9 in my early 20's, and I have a very small frame with long legs... For most of my life I have always looked very under weight. A few years ago, I gained alot of weight, and was actually overweight..... But I lost it all (it was mainly medication I was on that caused me to gain it).
I eat so much, and I'm not talking healthy... I'm talking burgers, pizza, junk food, etc. And I still look scrawny. ... I am constantly having people come up to me and look at me in disgust when they ask how I lost so much weight.... I can tell that they think I'm anoerxic. This is making me so self concious. I have gotten to the point where I dont even want to go anywhere because I hate the way my body looks.... IS there anything I can do to create more shape? or certain clothes I can wear?? anything...

1 week ago
I have started working out, but I feel like it doesnt do anything... I dont know maybe it just hasn't kicked in yet.... I'm still working on that though :)

eat a lot of carbs and protein and do a lot of weight training