I have work to do (I am busy).
I have a good job (I am successful)
My work is difficult (The work I do at my job is difficult)
They can also be used in the same way:
My work as a teacher is fun.
My teaching job is fun.
My job as a teacher is to allow students to learn for themselves.
My work as a teacher is based on allowing students to learn for themselves.
Do your job!
Get to work!
What kind of work do you do? -- I'm a doctor.
Do you have a job? -- Yes, I'm a doctor.
A doctor usually does not say "JOB" because "Job" is more common work. A doctor has a CAREER because a career is more important work.