Your production might be settling right down. Now that your girls are older and probably eating more real food as the main part of their diet they may be taking less milk which will in turn affect how much you produce. OR, they might be taking a bit more than they do normally and your body may still need to catch up.
You can increase your milk in the same way as you would when they were little, by eating well, resting (yeah, I know

) and drinking lots of fluids. Are you drinking enough water/juice/squash?