I have several concerns about my 20 year old house

There is a vertical crack on the 2nd (top) floor of the house Extending from
the top of the ceiling down about 3 feet. It seems to have developed
recently and this has been a wet and rainy season (washington state). The
crack look like a long thin V shape, no shearing. The widest space (top of
the V) is about 1 to 2 mm. I need to know what is causing this and how to
either reverse or stop it from getting worse.

Who should I hire to check/fix this problem? A civil enginner? A house
inspector? A general contractor? I prefer a "one-stop" shopping solution,
unless doing so would significantly compromise the quality of the solution.
I have the internet and yellow pages, but don't know where to look.