Yellow stains around window

Your window sounds like it’s not stopping the outside weather from penetrating in.

It’s water marks , very hard to get out , usually I apply a oil based gloss paint over the area let dry then apply finished paint

Water must be getting in somewhere, either from the window or cracks in the outside roughcast/render. The window might need re sealed with silicone

Hi I think the damp patches around your window and under you window sill is caused by the breakdown of the mastick on the outside of your window so its letting moisture in and penetrating water into the plaster, to solve the problem I would mastick the window and apply stain block on the patches leave dry for a few days then re paint that should solve the problem. Thanks mark

Sounds like some kind of damp. You can buy stain block paint to treat bad area then re decorate