Cause of damp in exterior building
Short answer is: condensation from not having insulation and openings to the outside. Not as short answer: If the wall and ceiling have little or not enough insulation any moisture that is warmed to a temperature higher than the exterior ambient air temperature will change to liquid water as it contacts the cooled inside walls. It will be visible as droplets running down the brick walls or door.   It will be most noticeable in areas of the room were the openings are greatest  (such as by the door you repaired). The problem can be reduced through: insulating the walls and ceiling, upgrading or improving the windows glazing, sealing any gaps and openings to the exterior and keeping the moisture level inside to a minimum.