I need motivation/ advice to tone my body/ lose some weight

I was obese about 3 years ago and got signed up for this diet program and lost 30-40 lbs. Now I am almost at the same weight that I was those 3 years ago and I am having trouble losing it. I try to workout but I just can’t find time for it. I weigh 165 lbs and I am 15 years old. I don’t want to lose more than 30 lbs but I would really want to tone up my stomach. Do you have any advice or ways I can get motivated to do this?