It's very common to have irregular periods when starting on LC. I've never had that problem, but ladies on another board discuss this at least once every two weeks when a new crop of beginners are confused.

As was mentioned above, you're dealing with insulin and glycogen. (I'm not a science geek, so forgive me for not being too technical in my next sentences.) It's also been said that fat cells store estrogen. As we lose weight, the cells shrink and estrogen is released into our bodies...which can cause some interesting "female" reactions.