Food sucks and I don’t know what to do, please help?

I 13(f) have recently been struggling with my mental health, I am suicidal and I constantly fall into self deprecating spirals over the smallest things like forgetting to put a cup away after using it. One of the main things that’s happened is that I’ve stopped eating as much, often only having one meal a day and even then calling it a meal is being generous. Food either just isn’t appealing or gross. I’ve never been bullied about my weight or been insecure, I was always at a healthy weight and have never had a bad relationship with food. But now my brain will call me names whenever I eat a normal amount of food, calling me selfish, that money could be spent on better things than feeding me, calling me fat or gross, etc. Yesterday I went out with my dad and since he was watching me I had to have a full meal to avoid suspicion. Almost immediately after I ate my stomach started hurting, badly, and I was struggling to go about the rest of my day, I also became very nauseous but didn’t throw up. Luckily no one noticed so it was fine, but I know it’s not a normal reaction. Today I found myself in a similar situation and the same thing happened, I know it’s not a normal reaction but am unsure what I am supposed to think? I was wondering if any on might have some insight? advice? or a explanation for what this might be?