Hello. Trying to make a change in any habit in our life is always difficult. You have quit smoking and it has been 17 days this is really commendable. Habits are hard to break because they have become a part of our daily routine and due to nicotine in cigarettes we develop a dependancy on them because of which quitting is so hard. To help you in this process and not cause distractions to your study you need to try and replace the earlier habit of smoking with something productive. Like exercising in the gym, meeting friends, or doing other such activities which you enjoy.