The brick wall at the back of my house is sinking. don't know where to look for someone to repair..?
Answers:
Look for a foundation and structural repair firm.
They repair sunken basement floors, driveways, house foundations, etc. Normally by injecting concrete beneath the existing mass to raise it back level.
Other answers:
yellow pages...builders!
yellow pages...builders!
news papers handyman and ask if they can do a new footer and bricks it may rtequire the ability to run a bobcat and shoring up the trench and then replacing the cement base of the wall
Call a brick mason.