Why am I gaining so much weight????

When I found out I was pregnant (at 4 weeks) I was 141.8....which is pretty normal for me. Today, at 8 weeks, I was 146.4. I eat healthy snacks (nutrigrain bars, raisens, yogurt, dry cereal), breakfast (either an English muffin or a granola bar), a small lunch (cheese sandwich), and one portion at supper. Even then, at supper I get full super fast and can't eat as much as I usually do. Why am I gaining so much weight. I've read that your not supposed to gain hardly anything during the first trimester. I'm so worried about my weight and what I will look like. Any answers?