Which pool are you using?

and are you sure you're configured correctly?

If you're hitting a low mining rate, and especially during a time when the network hashrate is high, your payout will be low and depending on which pool you're using, the payout threshold may not have been reached..

for whichever pool you're using, head over to their site and check your balance

It's difficult to answer anything specifically as I have too little info to work from regarding the pool. etc...