I have been taking 5 mg prn for 25 years. It is so individual. There are may weeks (usually not PMS weeks

that I don't need any. Then sometimes it seem like I go through a bottle in nothing flat. My doctor told me I was way too worried about it - some folks take 60mg a day or more, and my 5 -10 was nothing.
However, I do know that everyone is different. Just listen to your body. If you take "breaks" from it and don't have physical symptoms, then my guess would be that you are fine with it.