Why does the auto exposure button always overexpose my images even when the image is already overexposed to begin with.
This is usually due excessive clipping in the image (i.e. one or more RGB channels at 100% in a large image area). Simply lowering Exposure after applying Auto Tone will usually correct the issue. There's no way to analyze the file raw data using LR. If you want to evaluate some of the images for clipping you can download RawDigger free trial. BTW- The Auto Tone function was changed in LR5 to prevent underexposure with images that are heavily clipped.
I have also used the same version at work and I do not have this problem. I updated my lightroom to the latest version 5.7.1.
This is an indication that the monitor brightness setting on your work computer may be lower (i.e. less bright). Are either of these monitors calibrated with an i1 Display or Spyder device and if so are they calibrated to the same Luminance level? Lacking that there's bound to be differences between the two systems.