
You're right, it is usual for there to be bleeding when a bitch is in season, but some bitches bleed more than others, and some keep themselves very clean. Has she been cleaning herself more? Has she been weeing more when she's out? Those are both signs of incipient season.
If you dab her vulva with a clean white tissue every morning when she first gets up, you'll doubtless soon see a pink stain. Count that as Day 1 of her season, and remember to keep her away from other dogs for at least 21 days. Don't even let her alone in your garden.
:)