Is this normal?
in my experience, no,I have been playing everyday since 1974.
however i generally play in 30 to 40 minute batches. are u playing the two finger chords with the same finger or two different fingers.
my advice, isdont practise the same thing for too long, I find that with the 5 string banjo i limit frailing to 15 minute batches, otherwise i have muscular problems, however up picking because it is similiar to guitar fingerpicking i can do endlessly.