How to overpower all the negative thoughts?

delete all social media if youre using including telegram, keep away your phone at another room while studying and if you go to library then keep phone at home. make a plan with whole syllabus day wise schedule and try to stick on it till prelims. 

''Do yourself a favour and work hard now'',don't spend another year doing the same shit.

"Rest at the end, not in the middle."

There will be many answers you don't have, even questions you don't have. But you're going to keep going and figure these things out as you go. You have to continue to build that way.