Your situation is - unfortunately - common.
Look for:
pan flashing below the door threshold.
flashing over the ledger.
It sounds like this doesn't exist.
Rain splashes up from the deck and blows along the deck, putting a lot
of water at the line where the deck meets the main building. It takes
special care that's seldom given to manage the water.
I don't know of any books or web sites that address the problem.
Your best bet is a well respected contractor or an architect.
TB