for the last 2 months, I've been cycling for about 2 times a week and eating a little bit less. Last month I've been exercising(read cycling, jogging or hiking) for about 3 - 4 times a week and for last two months I've been exercising 5 times a week. I exercise for at least an hour.

I also drink about 2,5 - 3 liters of water daily.

For breakfast, I usually drink a protein shake at about 6am. Then, at around 9am I eat a portion of melon or watermelon. I drink black coffee in the morning. Then at about 11am I eat a can of tuna fish or another portion of melon or watermelon, or a portion of greek yogurt with blueberries. At around 4 - 5 pm I eat lunch, which is mainly proteins and vegetables ( I eat small portion of bread or something like that, but not everyday). Then I exercise, and after exercise drink one protein shake.

I've been eating like this for 3 weeks now and I simply cannot lose a pound, nor do I look "thinner" in mirror.

What am I doing wrong?