"under the weather"

Whenever someone says they're "under the weather," I immediately think "it's that time of month" even though I use the phrase "under the weather" for times when I've got a cold or other ailments because that was the context it was used in when I first encountered the phrase in some chapter book. However my automatic mental assumptions warrant a chuckle, while admittedly improbable & bizarre, especially when the person "under the weather" happens to be male.