5 pounds in 3 months?

is this a realistic goal? I'm 14 and ever since christmas ive gained about 5 pounds. I just want to get back into shape after sitting around during the winter and eating chocolate...lol. I was already really skinny before and im still skinny but i have a slight skinny fat thing going on. My flat stomach isn't completely flat anymore and im starting to get love handles/:. Im trying out for cross country after summer break ends and i wanted to start running and taking all refined sugar out of my diet. ( i already eat really healthy, the problem is aferwards, i eat too many desserts, so i already know i have to eat fruits veggies and whole grains +lean meats and proteins). What are some good running tips to get in shape and lose weight? Thanks!(: