Firstly, don't let anyone else tell you what you're feeling. These are your feelings and emotions and no one else knows them better than you do. So stop listening to you mum if she says you're lazy. 90% people don't even consider mental issues as something important and there is literally no benefit in explaining you problems to people who will never understand them.
Secondly, eating disorders are a huge issue. I myself feel like I'm developing one these days and it's kinda traumatic for me because food is practically my life. But I'm also dealing with anxiety these days to maybe your aversion(sort of) from food can be due to trauma(as you mentioned about your past) or anxiety. I guess, anxiety can be a reason. I don't know exactly what to advise you because I'm not a psychiatrist and i can never understand your problems better than you but I'll give you a few suggestions, that include–
1. Don't think about your weight. You are just 14 and this is the age where you should enjoy you life to the fullest rather than worrying about obesity or some shit. You can take care of your weight when you're 18 or above coz it's never to late to join a gym and of course what are gyms for?
2. Eat like your eating the love of your life (lol, don't take it otherwise). Treat food like it's the best thing in the world! You can start cooking as a new hobby and when you'll cook something the excitement of eating that will me more so that way you'll eat more
3. Find a person who actually respects your mental health and whom you can trust with your problems.
It's not easy to open up after what you've experienced but if we have to live then we gotta make some efforts to make surviving better. And lastly, I really really respect you for being so strong and amazing even after facing all this. You're one pf the bravest human I've even heard of. You're amazing and I'm not lying, I swear to my god. You are amazing and don't let anyone tell you anything else.