Like most medicines, amantadine works very well for some folks, and not well for others. It is pretty benign, though -- meaning it has very few side effects, and is an anti-viral, meaning my previous doctor used to take it to ward off viruses he might encounter during his daily job, not for it's "anti-fatigue" effect!
I'm told it takes awhile to build up in your system, and if it works for you, will work for awhile, then sometimes lessen in effectiveness, so you have to take a "holiday" from it for a couple of weeks, then start back up on it again.
I suspect it's probably a first line drug, meaning they start with something simple and without many side effects, and if it works, great. If not, then there are stronger/bigger drugs available.
None of these fatigue drugs seem to do much for me, so I don't take them, but lots of folks "swear by" amantadine. I'd probably try it and see if it helps. You can always stop later.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....