It's possible that if you have a larger percentage of fat tissue to lose, then there may be a hormonal adjustment as your body adapts to ketosis and fat-burning.

Estrogen especially is stored in fatty tissue, so as you burn fat, it is released into your system. Granted, it's a tiny amount, but it may be just enough to cause your cycle to be off for the first month or so, until you adjust. Possibly a few more PMS symptoms too .. .. but again, it's transient, and your body will adjust.

You might consider taking extra vitamin B6, and Evening primrose oil supplements as well, to help regulate, and ease cramping if that's a problem. If you take B6, make sure that you also take a daily supplement that has all the B-vitamins in it (taking just one B-vitamin alone will cause a deficiency of the others)

Doreen