There are many possible reasons for that pattern.
Medical – e.g. diabetes, anemia, thyroid imbalance, mineral and/or vitamin deficiency and . . . You should ask your family physician for thorough tests.
Psychological – like stress . . .
Physical – hard physical work etc.
Or maybe you are an evening person. Most of us are morning people, but some individuals reach best performance during evening hours.
It is another possibility.
Are you tired after night sleep? Maybe you are in place with heavy EMF exposition during work (school) hours?
If it is so than most likely your body response is related EMF exposition (overnight resting and/or during morning and afternoon hours).
More on tiredness and related information are here.