Theory:

As a matter of fact, every day in every way that little elf was a nag! Patrick was working harder than ever and was it a drag! He was staying up nights, had never felt so weary, was going to school with his eyes puffed and bleary.
Explanation:

Actually, that little creature was either troubling, complaining or asking Patrick to do something or the other all the time. Patrick was working more and more. Patrick was not able to sleep and was awake for many nights together. He had never felt so tired before and was going to school with his pale-looking eyes.
 
Meanings of difficult words:
  
Numbers
Word
Meaning
 1.
Nag
One who troubles someone all the time by complaining or asking them to do something.
2.
Drag
Something dull and uninteresting.
3.
Weary
Extreme tiredness.
4.
Bleary
Looking dull because of tiredness.
Reference:
National Council of Educational Research and Training (2006). Honeysuckle. Who did Patrick's Homework - Carol Moore (pp. 7-10). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.