Help needed: my texture becomes more corrupted the more i paint it.

I am painting a texture using the default soft brush, not using any other features, and it looks fine. but then when i move to a different part of the mesh to paint, these tiny dots appear on the parts i painted previously. They appear over time, and always when i'm not looking. I cannot make progress on my texture as going to fix the problem in 1 spot makes it appear on another.