I hope you have met a psychiatrist and are taking medicines prescribed.  They would be helpful.  After same, please visit a clinical psychologist trained in cognitive behavioural therapy  to help you in overcoming your  obsessive thinking .

Dear sir, Please realise that obsessions are a treatable condition and you are unnecessarily putting yourself through so much suffering. If not treated, obsessions can also lead to depression or psychosis. I suggest you please meet a psychiatrist at the earliest and get treated. You have ample of options between medicines, relaxation techniques, thought stopping techniques and behavior therapy. You may opt for any, as all are equally effective.

I am sure it affects your studies too. All it requires is some clarity and some discipline  which would help you to come out of it easily. Di consult a Psychologist /Counselling your city and be successful of your wish or dream as a challenge.