What are the possibilities to this?

[JamieC]

Okay so my cat has had diarrhea for a couple of weeks now. Thinking it was the flu(she tends to get this at least twice a year) we let her alone. But it never has lasted this long. What else could it be?
Another question. My other cat has been licking herself bald by her rear end and I was wondering if they brown spots on her skin are normal?

Thanks in advance!