I need help with weight gain?

Kayy So My Name Is Shelby Im 12 Years Old And Im A 7th Grader, I Went To The Doctors Yesterday And They Took My Weight I Came Up As 111, Is That Really Bad?? I Mean Im Turnin 13 In Like 2 Months But Still, Is It Bad?? I Have Been Drinkin Water And Diet Coke Only. I Only Eat Reagular Food For Dinner, Everythin Else Is Special K. I Exercise Everyday, I Eat Fruits And Veggies. I Run 2 Hours Eachday. I Do This All The Time, And I Only Been Gainin Weight. I Have Took Diet Pills, I Have Had Eatin Disorders. But I Cant Figure It Out. Im Not Pregnant, I Am A Virgan, But I Hadnt Had A Period In 4 Months. I Cant Figure It Out. Can U Help Please?? Also, In A Month I Gained 8 Pounds.