Can you post a screenshot of your layers panel.....your question is a little ambiguous so the more info you can give us the easier it will be for us to determine what the problem is...and hopefully resolve it for you.
I appreciate you may not be familiar with the correct terminology but if you can try to be as close as possible then it would help tremendously.
" ...where you can see what's not been painted... " doesn't really mean anything specific in PS.
PS - I just re-read your post. As far as I know, layer masks can not be transparent. They are either black, white, or some shad of gray in between those two extremes, but they do not support transparency. So, you will never see the usual checkerboard to indicate transparency if you are working on, AND viewing the mask.
In contrast, if you were painting on the layer mask, but viewing the actual contents of the layer (ie, NOT viewing the layer mask), areas where the mask has been painted black will be represented as a checkboard, indicating transparency of the contents of that layer in that area. This, of course, assumes no other layers are turned on.