Maybe the diff is increased. When the diff was low (for example 1), you had to mine 100 "share" at 0.1 diff, than you can see a share in the pool.
Now that the diff is increased (1->100 for example) have to do more complex work, so it use more time to resolve the work.
You can try mine at lower share. If you get 4 share every 60sec you are in the right way