To be a healthy female guppy is usually to be a pregnant guppy. :)

The only females over 2-3 cm which are not pregant are those the from a tank where the aquarist carefully removed young males (as they "sexed out" or showed adult phyical features) from their batch of youngsters. That way there would be virgins and it would be easier to selectively breed them.

Since female guppies can carry sperm from matings which can be used to inseminate batches of fry for over six months (and six or more batches of fry) they are probably already "with child."

That doesn't usually stop males from wanting to mate. They are (ahem) highly motivated to do so. (Sort of a hormone attack.)

Studies have shown that it may make sense (from the perspective of keeping a specific male's line going) to continue to mate. Newer sperm stored in the female's body will produce fry, sometime in greater numbers than seed from older matings.!

If you have had the guppies for over a month and have noticed females getting "broad of beam" and then thinning out, they are dropping babies. Whoever your tank residents are, they are enjoying a guppy fry snack.