Can I loose weight even though I'm not fat?

I am 15 years old and I weigh 47-48kg I used to weigh about 43-45kg but I've gained alot of weight lately. �I'm about 153cm in height. I've been eating healthy (No junk food/drinks) and treadmill for 30 minutes everyday. Will I deffinitely loose weight or is it all pointless? ��