3 weeks after sleeve, not much weight loss, what's wrong?

How much is not much. Many factors determine the rate of weight loss.. What was your starting bmi, the higher the starting bmi usually the more rapid the weight loss. Are you eating enough? It sounds counter-intuitive but eating not enough can actually slow weight loss. Also, mini plateaus of a few weeks where you continue to lose inches but the number on the scale doesn't move are very common. Talk to your surgeon..