If you have a crawlspace with an earth bottom, it's possible the humidity is coming up through that--check whether you have a vapor barrier below your house. You probably don't, given the age of the house.
Getting a dehumidifier is definitely a possibility. Or a 'swamp cooler' arrangement, where cold water is used to make condensate that you then pipe out of the house, but that really only works in higher temperature air.
we have a similar problem with our house. so far we have found it has helped a little to get fully-vented soffit and roof ridge vents. this allows the outside air to move through your attic to vent the humid air.
condensation is a problem of insulation. the cold from outside is allowed to cool (either windows or poorly insulated sections of walls/roof) and the warm humid air inside condenses on the cool sections. if you have condensation on windows, you need new windows. if you have condensation on walls, you may need better insulation at those points.