okay, this is probably a "dumb" question, but how do you know what suction and speed are best on the medela PIS? my nipples are very sore. do you think i am doing something wrong with speeds? i use the suction about halfway up and always use the fastest speed... i am getting about 9 or more oz. most times i pump (for 10 -15 minutes). any suggestions on how to tell what suction and speed i should be using are welcomed. thanks!