solving damp problem?

Before redecorating the front bedroom last year, I noticed a small damp patch that looked to have dried out in the bottom corner(this is where the front of the house meets the gable end).had the room replastered(skimmed)and now the damp seems to have come back.its about 5" above the skirting but nothing has appeared in the top of the corner and nothing below in our living room.had soffit's and facias renewed and chimney stack dropped below the roofline.But i think the problem was there before work was done to the room. Any advice would be appreciated