Damp Inside After Painting Outside With Standard Emulsion

[Wyan]

Hi, can anyone help? We have a pre-war house with pepple-dashed rendering on the upper half. A few months ago I undertook the laboureous task of painting the rendered walls, which I did with a standard emulsion. Soon after speckles of damp started to appear on the inside wall, which has now worsened.
From what I have read since, it seems I've probably made the mistake of applying the wrong paint / too thickly and the so walls can't breathe. My question is therefore what do I do now? Do I need to remove / reduce the paint on the outside wall, if so how; vent it somehow; damp-proof paint the inside? Advice appreciated.