How often have you changed your bedding?
How often do you feed them?
How damp do you keep the bedding?
Do you cover it with news paper?
What do you have your worm bed in?
With these answers you can get a better ideal of what your issues may be? I have red Wigglers that get as big as a pencil in my beds. And right now both of them need redoing. But I feed Corn meal every day and sprinkle it with water. I know people tell you no to wet the feed. But I only feed 1/4 cup per bed per day. This when dampened and covered with news paper. Allows them to feed and grow bigger and faster.
Pete