Why do white patches/spots of white appear on my wall?

I painted my room a month ago and slowly, white patches or spots started to appear. Even when I repainted the area with the same paint, the white still reappear! Thinking that the problem lies with the paint brand, we repainted the room with another paint brand. And guess what? The white appears yet again! It's so frustrating! Please help if you know what I should do, thanks in advance.