Struggling with Eating Disorder and Family Pressure

I did good today, until just a few minutes ago. I try to stay within a healthy amount of calories (900-1000) because if I drop weight too fast my mom will force me to eat. I usually have just plain yogurt in the morning, but my mom made me breakfast which was kind of her but I was screaming on the inside, tons of fat and grease. But the rest of the day was good. After dinner, I ended up eating 999 calories all day which is more than I'd like but again I can't lose too fast and I'm afraid of making my body go into starvation mode and hoarding fat. Then after dinner everyone else was making a sandwich and my grandma made me one, and if I don't eat something that's offered to me they get mad at me. I went 150 over my goal and I felt so bad. I ate 2 more sandwiches and 3 packs of chocolate donuts and purged it all including dinner. Even though it's all out of me I feel like my body still absorbed all the calories and I'm just going to get bigger. I need to stop this.