45 minutes is a long time to be pumping and still feel full on the sides! It sounds to me like your pump is not triggering a very good let-down, so I would try another pump. As someone else said, the Medela is good. I also liked the Ameda. Make sure the flanges (cones, horns, whatever you call them!) are the right size for your nipples. The whole areola should be sucked into the cone when pumping or it will really start hurting. That being said, three ounces is an awesome start! Best wishes with everything!!