both walls cold, so moisture in the warm air cools and condenses on em..
specially round the window....
fit a vent like flynny says but theres things called 'passivents' dont get a draught, drill a 4" core out near the ceiling and fit through, theyve got like a bung in that lets moisture out but no draught etc..
or insulate the walls as well dab some insulated board up, stop em being cold surfaces and the moisture wont condense on em..