I have a PISA, and i have been using the breastshields that came in the 'kit' that we purchased at the hospital. yesterday I bought, at target, the medela breastshield/valve/membrane kit (i was surprised b/c in this kit the horns don't disconect, it's all one big piece? KWIM) anyway i have lagre breasts, 36 E or F currently and i have never been sure i'm using proper size breastshield. it's always been a little uncomfortable but hell it's a pump. this new breastshield felt like it was cutting into my skin, i cried out in pain and almost ripped it off before turning the pump off. it didn't hurt on my nipple but rather where the edge of plastic hits my breast? make sense, anyway i've been searching online all day to no avail, how do i know if i am using the right size, i've read instruction but i cannot really tell if it's right or not.... i need specifics, examples, pictures even??? where do i go???