When you've been doing something awhile, you've been doing something for an indefinite amount of time: it could be a little while or a long while.
This is a word that's hard to figure out without context. Awhile always applies to time, but the amount of time can be small or large. You could say you've been waiting awhile in line at the bank: that might mean 15 minutes. On the other hand, if you haven't heard from a friend in months, you could say, "Wow... It's been awhile!" Like a bit or a load, you can't measure awhile.