Question about Birth Control?

I want to start using birth control, but i was just wondering what kind of side effects do you get when your on it. Like how does it affect your period? Will I get moody and emotional if I go on it? Does it affect your appetite at all? Will i get sick or anything from it? I dont really know much about it at all, so any information will help. Im just worried to go on it because I already have this health problem where i can only eat like one small meal a day, and i throw up about every week or two, and i just get sick a lot. Iv been to the doctor about this, and it wont affect me going on birth control, but i was just wondering if getting sick is a side effect of the pill? Because I dont want to get sick even more then I already do. Another thing Im worried about is getting really emotional. Iv been depressed for about a year now, and I cry a lot and stuff, so would going on the pill make that worse, or make me even more emotional? Thanks for the help :)