A native English speaker might use this expression in spoken English, but it is very colloquial. In rural areas you may hear this type of expression in spoken English. This would not be standard written English.

No, it should read: I work as a teacher. I have done so for four years (now). or simply I have worked as a teacher for four years (now).

No, it should read: I work as a teacher. I have done so for four years (now). or simply I have worked as a teacher for four years (now).

No, it should read: I work as a teacher. I have done so for four years (now). or simply I have worked as a teacher for four years (now).