how do I get back to my usual weight

I'm 16, two years ago I used to weigh 116 pounds I was 5'7 . I then went through alot of stress and went down to 100 I was told to gain weight so I did unknowingly until I got up to 145. I want to get down to 125-130 but it's not working. for over a month I have been walking 4Km's five days a week and eating better I'm sort of slimming down but my stomach is becoming a big problem how do I lose the extra stomach fat and get down to the weight I'm used to.