Weigh Loss??

I've been dieting for three days, (not a long time, I know.) And I have been working out slightly. I walk white often at school and I do a bit of running when I get home. So, why am I gaining weight instead if losing? I'm 17, 5'3 1/2, and I used to weigh about 179, but now I weigh 180. I know isn't a big difference but, eh. Anyway, I'm consuming 1200 calories or less. I drink quite a bit of water. Why am I gaining instead of losing? Will I start losing eventually? Is this just part of the jorney or..?