Not having a great day at all

Today started ok enough. I went to class at 8am. I took a diet pill and got a little jittery. I finally picked a topic for my persuasive speech that my teacher approved of. After that class, while waiting for my next one, I sat outside and smoked while reading my book. (A Bright Red Scream) My next class was extremely boring. When I got home things were ok. I had been fasting for 14 hours but I was getting really sick and REALLY hungry so I thought I could have a few chips with dip. When I was getting it, my father-in-law asked if I liked sausage gravy. I said no and in passing said I could cook my own dinner, meaning that he didn't need to worry about me. He got really defensive and angry. He asked if it was just the food he was cooking that I had a problem with. I told him no that I just didn't like eating. He then pointed out I was getting chips and dip. I got upset and said, "I know, I eat too much. I have a problem." I was so upset. I walked back into my bedroom and started crying. My husband asked what was wrong and I explained everything to him. Why can't people just let me eat the way I want to? Why does it have to be everyone else's business? I've had people nit pick at what I eat since I was in Elementary school. I eat too much, or I don't eat enough, or I don't eat the right things, or I don't eat often enough. I'm 21, why is it so hard to let me choose how I live my life. As long as I'm not dying, I don't see any problem in it. For God's sake I'm 5'3" and I weight 150something effing pounds. If people would just leave me the eff alone, I'd be able to get my weight down. I don't care if I do it in a "healthy" or "safe" way. Let me be a grown up. If you want me to be able to take care of myself, let me start now! Gurr. . .  I'm so frustrated and upset. I want to cut so bad. I scratched myself twice already but it's not the same. If I could just get a little time alone, I'd be fine to get it done and cleaned up and no one would notice but now everyone is hovering. I don't know what to do.