Why Am I Not Losing Weight? How Can I Lose The Last 25lbs?

I'm honestly starting to give up now. I've been exercising for 3 months straight (almost everyday) and I haven't lost a pound. I know it could be my diet. I honestly cant say I have a real "diet plain" because I try to take tips from everything I read and watch on dieting. I don't know anymore. I'm a 14 year old girl, I'm gonna be 15 in 3 months. I weigh about 140lbs now. Last year I weighed about 165, I lost 25lbs in a year. I want to lose another 25lbs. But its not working. I need a diet plan that will me, I guess..? Has anyone have this happen to them? What do you do to lose the weight? What is a diet plain and workout that works to lose this weight? I don't really know what I need to do to do this right but I need to lose these last 25lbs already and I need help. PLEASE HELP?!