A.V.
Have you tried a different type of pump horn or a different size? Have you tried a different intensity? You might want to take your kit to an LC's office and ask to be measureed. I had to change to a different sized horn. because my skin was rubbing inside and making it raw.
And, I hate to say it, but if it continues after all that, you may want to ask your GYN for a referral to a breast specialist. My friend felt that something just "wasn't right" and ended up finding out she has inflammatory breast cancer. Bottom line, if it's not right, keep asking til you get answers.