If you have set wrong suction setting then it can cause pain. And moreover suction that is too hard can sometimes cause trauma to the breast tissues. However, this usually doesn’t last long. Pumping too much and too often can disrupt the milk flow. Filling your body with unnecessary breast feeding hormones, and block milk ducts leading to other issues. If your body is signaling pain, then stop pumping milk. If you ignore the signal and keep on pumping, then it can cause severe damage.