Wat is d reason for this demotivation? Remedy?

Dere is demotivation goin on in my life b it work life or studies n dont think it is just an ordinary one. Wen i m motivated using some affirmations i can study for 12 hrs/day but wen i m demotivated i dont feel like studying for 10 min (DIS IS D SCENARIO ALL D TIME). Despite having many urgent needs in life 2 fulfil or my dreams i dont get d motivation. For the last 4 exams this is happening 2 me dat despite knowing i can do very wel in xams i dont study due 2 dis n eventually fail badly. Dis is not a new problem but is wid me since as far as i remem. My psychologist diagonised me wid Body dismorphic disorder n i have improved a lot from this disorder 80% approx but this demotivation is still the same. Dis causes serious problems in my life like hopeless feeling, frustration, sleepiness, weakness etc. I want to succeed but dis is stopping me. N 1 more thin i dont find this type of demotivation in anybody around me. PLZ HEPL ME I DESPERATELY NEED IT N TEL ME SOME PRACTICAL SOLUTIONS.