Why didn't I lose weight this week?

I'm 5,4' and 115 pounds. I decided to up my calorie intake from 1200 (where i was losing about a pound a week) to 1500 last week(still intending to lose weight), and i exercised 6 times a week for at least an hour every day. Yesterday, I had tennis camp, which was about 5 hours of tennis, so i upped my intake to 1900. But, today, i weighed myself, and i stayed the same weight as i weighed last week! I know my metabolism HAS to be faster than that, because i'm only 15, and i'm exercising so much! Why didn't I lose any weight?? I want to be able to eat about 1900 daily to maintain, which i feel is realistic, but why am i maintaining weight on so little calories???