Looks like the answer depends on the context! http://www.spanishdict.com/answers/279630/qu-significa-vaya-faena The sentence prior to "Vaya faena" seems like only a snippet of the full sentence but what's there seems to be like "with the health of iron that you've always had!" It's supposed to be like what a mess or what a problem in reference to something really tedious and annoying. Hope those point you in the right direction if they don't answer your question!

'vaya faena!' sounds like an arcaic form of 'que trabajo!'

you should replace 'faena' with 'work'