Any help appreciated.

We have a 12 year old calico cat which recently was diagnosed with a bit of
arthritis in the rear legs but otherwise in good health.

About a week ago, 'it' stopped letting people touch her front paws - really
hissing as if sensitive.  We left her alone a few days but now she won't lie
down...just sits up (the Egyptian cat look) but keeps shifting from paw to
paw.

We took her to a Vet, but other then a bit more than normal 'red' look to
the paws (normal temp) he was at a loss...suggesting that when he sees
things like this, it is due to a burn or something new mopped on floors and
rugs (neither of which we have seen or done).

He gave her a light pain medication (usually reserved for cleaning teeth and
such).

Since then she does seem more comfortable, but now seems to have stopped
going to the bathroom....BUT otherwise in good health (drinks and eats OK).

Still sensitive on the paws.

Does anyone have ANY idea what is going on here?