Agony after expressing... how do I choose the right size breastshield?

[Etwinkles]

I am struggling to express because of pain. I have never managed to express very much... probably averaging 30ml out of each breast when I express instead of breastfeeding my twins (have tried at various times through the day and night and can last about 10 minutes before I can't handle it anymore). If I express after breastfeeding them, about 10ml out of each breast. I was using the Medela Symphony but now am using Medela collection kits with the SpeCtra double breastpump. I tried to look online for info and thought I might be struggling because of using the wrong size breastshield but found the diagrams on the Medela website confusing. It seemed to suggest that pain and low milk volumes meant I needed a bigger breastshield but the diagrams seemed to suggest I needed a smaller one. I started with the 24mm but after 10 minutes I'm in absolute agony. The tip of my nipples go white and they burn for ages. I have now tried the 21mm but hardly managed to express anything at all and still had the burning pain, but not the white tips. Can anyone advise me on how I can know for sure which size to use? I don't want to spend any more money on other sizes without knowing for definite. Maybe it's not the breastshield at all?

Anyone?

Expressing with twins... . Maybe you have the pump turned up too high. I found that longer pumping and less pump pressure was better. May be turn down the pump, think happy thoughts and try to not look at the bottles. I listened to the radio and chilled out (much more milk that way).

Good tips, thank you.