new shape keys affecting old ones

I’m adding shape keys to a face model for wrinkles, and I’ve run into quite a problem. I made the first shape key, and everything was fine. Now everytime I try to make a new shape key, it not only makes the new shape key, but also adds the new shape key to the first one, so that when I drag the slider on the first shape key, it makes the changes from both the shape keys. How so I add multiple shape keys without this happening? I have been working on this for hours now and I can’t seem to get blender to do anything different. Any help would be greatly appreciated.

First thing I’d check is that you have Relative selected and each shape key should be relative to the base, not another key
If that doesn’t help, it would be easier to correct if you attach a blend that just shows this problem.