rainwater leak through wall into bedroom

[Daniel3103]

Hello,
I'm posting here to ask for advice about a rainwater leak into my bungalow. Rainwater is leaking through the external wall into my bedroom. I've already tried to fix the leak twice, and each time the fix has worked for a while, but the leak keeps coming back. I'm not sure what to do now.
The leak that I see happens when rain falls. The water comes from the top of the window recess inside my bedroom and falls down onto the floor. I'm pretty sure the leak is through the wall not the roof (because there are cracks in the external wall, whose location outside matches the ones inside where the water drops from; because I get the leak when the water falls at an angle onto the wall but not onto the roof; and because I can't see any leak in the loft space). The wall is a double wall made of concrete blocks, with a cavity in between, and the outside is rendered. As mentioned, there are visible cracks and holes in the rendering. I have patched those cracks and holes with cement on two occasions, and each time it has sorted the problem for a while, but the leak keeps coming back. I need to try another way to fix it now, I can think of two possible approaches but I'm not sure whether either of them would work well so I'm opening up the discussion.
The first approach I'm thinking of would be to get a professional to patch the outside wall. Would this have to involve removing the rendering to treat the wall underneath, and if so what would the professional need to do? What type of tradesman or builder would I need to contact? Could I leave this part of the wall without rendering for a few years? (I'm asking this last question because the whole bungalow is a renovation project, inside and outside, a lot needs to be done including the whole rendering but I'm trying to do one thing at a time and the rendering is not the top priority; I'd rather not put new rendering on until I get to this point, but I still need the leak fixed now because the dripping noise is keeping me awake at night.)
The other approach I'm thinking of would be to stick a sheet of waterproof material on this part of the outside wall, as a temporary fix for a few years before I renovate properly. Are suitable sheets available? Would I be able to stick one myself or would I need a professional? Would the noise of the rain falling onto the sheet keep me awake too, as this is outside my bedroom window?
So, would either of my approaches potentially work, or would you do something else? Is there something else I need to know?
Thanks for your advice.

[Gadget]

Photos would help..