I don't know if you have this option turned on in Photoshop....so it makes the preview icon and preview thumb etc.

When it is turned on, it basicly saves 3 copies(in different sizes) of your image...making your file size bigger than it needs to be.

If you turn it off (in photoshop prefrences) it will reduce your saved file size. This might be what is happening to you?

No more nice little preview icons, but a good naming scheme will take care of that.

-my 2 cents