Extreme fatigue and tiredness. I do?

Hi. I have been on Nexito 5mg for the past 8-9 months. There has been considerable improvement in my mental health but with weight gain. I have been preparing for some competitive exams. For the past two months , i have been feeling extreme sleepiness in the morning and throughout the day. Now its the last leg of my preparation and i cannot waste time feeling drowsy so i started with Modalert 100, which my psychiatrist advised when i initially started but made me stop it after 3 weeks. I didnt consult my psychiatrist for starting the med again.  Right now, i am feeling extreme fatigue and weakness. This is affecting my studies. In order to solve one problem, i have landed on another. I donot have time to start and get accustomed to new med. What should i do?