If you have been on diet
for three weeks you should not expect to see much.
3600 cals in 1 lb of fat. Daily caloric requirement is about 1800 cal/day. If on a 1500 cal/day diet you are losing 300 cal/day. Therefore 12 days per 1 lb wt loss. In three weeks maybe 2 lbs. This is less than the accuracy of your scale and normal wt fluctuation. Keep it up. Write in 6 months with 15 lb loss.