I Don't Understand-it's hopeless!

For 2 weeks, I have been dieting. staying from 1400-1500 calorie. 2 days I went over to maybe 1800. but I have gained 2 pounds! I do exercise videos every morning, bike almost everyday, and try jump roping a few days a week. How am I GAINING weight? Back in April I kept to 1300 calories but did light exercise and I steadily lost weight. How am I gaining it now?

Please can anyone give me help, suggestions, feedback, advice. I try cutting back on my sugar and making healthy choices. I don't do this all the time but I am slowly starting to make changes.

today I did an exercise videos that sued weights. It really made me sweat. Everyone says to use weights because you'll be replacing the fat with muscle and it'll burn a lot of calories. But last time I did this i ganed 2pounds and then stayed there. I use light weights withhigh reps. Can anyone give me advice, feedback, suggestions on weight lifting?

I feel so hopeless and stupid! why isn't anything working?

Backround information: I'm 13, just about 5'5-supposed to grow until 5'8.