I felt so depressed,tired and motivated.Please help me

Hi,I'm a seventeen-year-old girl.I really need your help because I really don't know what's wrong with me.Last week,I passed an extremely important examination with flying colors. At first I felt so happy and satisfied that I felt like there was nothing that could stop me from trying for my next targets.But just few days after my success,I feel so terrible.When preparing for the exam,I used to stay up late to 2 a.m during months to revise my lessons,but now,I can't concentrate and do my homework.I keep crying and feeling tired,unmotivated and lazy.Even I think about committing suicide.I set many other targets and draw many detailed plans for them but I just can't carry out.I tend to spend some days taking a rest as a gift for my efforts.But I can't because I know I will feel really guilty when wasting my time like that.In fact,even before my exam,I also felt so tired and depressed but I still tried to go on.And now,maybe I'm completely exhausted.I really don't know to do.Can someone give me advices,please?Thank you so much.