I can only erase or darken what I've drawn, no matter which layer I choose or create

[Loganschafer]

I'm drawing a cartoon, I started on the character first. I used a bunch of layers to create her, and now I want to start on the background, I saved it and then revisited it the next day to start on the background and now I can only erase or darken the lines/shading I've already drawn, I can't draw anywhere I haven't already drawn, no matter which layer(s) I select or deselect. I've had this problem on a previous project too and I couldn't figure it out so I just gave up on it. I've looked all over the internet for the solution to this issue and I cannot find answers. Please help, I will give more info if you need it

[Ussnorway]

we can't help you without something to work with... can you share the Psd file?

[Chuck Uebele]

It would help to see a screen shot with the tool your trying to use selected. It sounds like you have the brush's blend mode set to darken or multiply, rather than normal.