We need more history. Are you young and just haven't filled out after your last growth spurt? Or is this new for you and you used to weigh more?
I was just like that when I was 15 to 25. I ended up having Celiac disease. Now that I'm an adult, my best weight is about 124, so you aren't necessarily far off.
The important thing is whether your thyroid is okay and you don't have a digestive/absorptive issue like Celiac disease. Try to keep snacks with you like low-salt healthy nuts so you can keep your blood nice and even all day. It's unpleasant to be too hungry when you have no body fat to support you. If you don't have food issues, enjoy ice cream and milk shakes while you can, but most of your calories should come from healthy food with lean meat and lots of vegetables. You can safely ignore all the warnings about bananas being fattening, that's for sure. Do not let your weight rise quickly. A good indicator is how your clothes feel and how your energy is. Thinner is easier on your body.