Well, you can do what you have in your list so far for a month and see how you feel.

You can add Morton Epsom lotion applied to your legs once a day... and use that as your magnesium source. A quarter's dollop divided between your lower legs each night will show if magnesium is your main need. Walmart carries this, Walgreen's and online at Amazon.

But I suspect you may need carnitine... acetyl carnitine helps with mitochondrial energy production when the mitochondria in the cells are damaged.
You may try this after a month if you are still having the muscle weakness. Starting at 500mg a day and increasing by 500mg a week to a upper level of 2000mg a day.

If that doesn't help within a month or so, no need to continue with it.