Please don't try some of the advice mpau0516 is giving you! In particular, don't try to remove the battery. You have a very recent MacBook Pro, according to your profile, and its battery should never be removed by the user, only by Apple techs. Not to mention that an SMC reset (which is what the steps he gave you involving the battery would do on an older Mac) will not help with your particular problem. And absolutely do not download a copy of TuneUpMyMac... that kind of software is worthless.
As to what you can do, from the sounds of things, your hard drive is probably damaged. You should try repairing it with Disk Utility.
If Disk Utility reports no problems and the drive remains full, do you have a backup or something that you can boot from? If so, start up from that backup and download a copy of WhatSize and use its Measure as Administrator function to determine where the space is being used on the internal hard drive. Alternately, you can use OmniDiskSweeper and then, after placing it in the Applications folder, open it by pasting the following command into the Terminal (found in the Utilities folder in the Applications folder):
sudo /Applications/Utilities/OmniDiskSweeper.app/Contents/MacOS/OmniDiskSweeper
After you paste in this command, press return. You will be asked for your password... enter it, and don't be surprised when nothing appears when you type. Press return again and the program will open with admin permissions, so it can look in folders that would otherwise be off limits.
Once you have done this with either program, don't delete anything, but report back here where all that space is being used.