Is it normal that i am less motivated in school?

so my freshman year was fantastic. i got all A's and one B. i was motivated i was enjoying school and things were looking good. my sophomore year was more difficult but not to the point where i should have been doing greatly worse. i was still motivated but not as much. my grades turned out so so. 3 A's 2 B's and a C. now im in a new school and it's my junior year. the most important year of my life! i am so distracted, im acting out my grades are shit..is this normal?