This sounds a great deal like you have a fungal infection of your toenail. The fungus that causes toenail infections is found in areas like shower stalls and gym locker rooms and it is relatively easily picked up. It causes symptoms just like what you describe, namely discoloration, distortion and thickening of the toe nail. It could be that the nail became infected when it was damaged all those years ago, as this gives an opportunity for the fungal to get in under the nail bed. As you are experiencing, these infections are very difficult to treat and rarely go away on their own, often lasting for many years.
There are many over the counter treatments for fungus and many home remedies as well. However, basically none of these are effective in treating established toenail infections. The only effective treatments for these infections are prescription antifungal medications which are taken by mouth over a period of several months.
I suggest talking to your primary care doctor
as soon as possible. They will be able to confirm the diagnosis of a fungal infection and they will also be able to prescribe the necessary medications for you so that you can get this cleared up.