WHY AM I GAINING WEIGHT!?

ok so I just turned 17 and last summer i was very skinny i am about 5'4 and i was 105 pounds last year. I didnt realize it but i really wasnt hardly eating anything maybe 700-900 calories a day and i am a very healthy person so those calories were like from fruits and protein and chicken and veggies. so then i got over not eating a lot and depriving myself so i sstarted eating kinda normal again. It's been about a year and im now 130! i have no idea how i gained so much weight i still refuse to eat junk food i dont work out (never have) but i eat about 1300 calories normally a day maybe less and ALL healthy food except for occasional frozen yogurt, why am i still gaining weight!