Kirsten - Big ! Ifind it difficult enough with one; let alone three! It is so hard with breastfeeding; you never know how much they are getting... Do you get Ben weighed at all? If he is putting on weight, you can stop worrying about your milk... Maybe contact a lactation consultant? I'm having trouble too with my supply; the paediatrician put me on Motilium (tablets) and now Jasper puts on 250g a week!
Hope you'll be able to find the right support! Otherwise it is not the end of the world to start Ben on formula...