Pictures imported from my Nikon D3300 into light room come in darker than what is shown on my camera
Have you set the camera to use Active D-lighting?
This will affect the image you see on the back of the camera (which is the raw file's embedded jpg, not the raw file).
Any kind of special camera setting like this will not carry over to Camera Raw.
I suggest you turn Active D-lighting off, and take a look at this thread for more details. It's in the Lightroom forum, but also applies to Camera Raw.