Take the first and easy step to make some conclussions to what could be the problem.
Tired hands, tired muscles, both need energy, so what are you doing to supply that energy?
Before playing you need to stay hydrate you need water in your body to supply the muscles. Yon need energy foods, food that release the energy gradually not just give you a boost.
Foods like oatmeal, pasta, brown rice, fruits, etc will all give you a great source of energy.
But beware of eating heavily before gigs, the blood supply your hands need to transfer this energy will be working on your digestion so eat light in the hours before playing, almost snacking if you like...small bits of food over the time, before, during and after the gig. If when it is over you want to eat heavy then go for it.
Alcohol is a not a good ides as it de-hydrates, so negates the bodies need for water. Alcohol does not hydrate it de-hydrates, and that is bad for muscles as you lose essential salts and minerals every time you go to the toilet.
Warm up you hands with some gentle stretches and easy playing, arrange you set so that songs "warm up" as well, the more the set goes on so the harder the songs demands on the hands...ease into it.
Try these things and if after a couple of months you are still having problems come back with the new information on how things worked out....better or for worse.
