Why does weight loss seem to "plateau" for a view days sometimes?

I don't get it, i'm a guy i am 5'11 and when I started working out I seemed to lose weight steadily. I was 343 lbs. when I started, now i'm 314 so far but for the past 4 days i can't get down even one pound??? My diet has not change i'm still consuming 1400-1600 calories a day, i'm still "fat" so my workouts aren't near what they should be but i am doing more each day. I hit a speed bag for 15 min. a heavy bag for 15 min. i do reg. curls, hammer curls, sit ups, and planks. What could cause me to not lose anything for the last few days?