Need a way to maintain my weight?

okay, so i'm 13, 5'5" and a half and 129 pounds. i have recently lost like 80 pounds in a span of about 7 months and now i need a way to maintain my weight. everyone keeps telling me i'm going to gain it back if i keep going how i am and it scares me. i don't want to gain any back. everyday i have a bowl of honey bunches of oats with pecans with skim milk and then for dinner normally a cup of yogurt and berries or one cup of progresso vegetable soup. i don't eat lunch because normally i don't want to. i do 20 minutes of intervals of brisk walking and running everyday which is about a mile and a half. i don't want to change much but i refuse to let myself gain weight back and i just want to stabilize my weight. and i am trying to be a vegetarian. please help