This means: His urethral tissues from her G-spot to Epicenter was not fully engorged when you applied a heavy pumping to her vaginal ceiling. That is, your pumping over-stimulated(irritated) her urethral nerve. The urethral, G-spot and Epicenter nerves must be in the hormone-reriched blood bath to absorb the stimulation shocks, and heated up by the testosterone burning in the local hormone receptor tissues. In other words, her vagina must be fully expanded before heavy vaginal pumping.
You should start from screwing and soft pumping for 10-15 minutes and make sure that her clitoris and G-spot is swollen to an extreme, as shown in
http://www.actiontao.com/image/lovetool.jpg