Hey Kim!
A couple of things: Yes, monthly stuff slows down the scale but will probably pick up quickly right after. Next, the scale won't always move.

This may seem obvious but you can't get nervous if you lose four then nothing for a couple of days. Your body is adjusting and losing what it can. Try to stay on your Saturday weigh-in schedule - that way you can't be affected by the days where "nothing" happens.
You're doing great - just hang in there!
Kat