When I upvote an answer, a message shows up saying "You haven't voted […]." It just fades out so fast that I am unable to get the full message.
What's that message? Why does it fade so fast?
it is :
You haven't voted on questions in a while;
questions need votes too!
Look at the blog entry : Vote For This Question or The Kitten Gets It for more information.
It says you haven't voted much on questions. That means you are getting close to running out of answer votes but do have some question votes left.
Here is the question that relates to the change of max question votes: