Pain during .Suggestions please?

My gf complains of pain in the lower part of the . It is concentrated at the lower edge of the (the edge near the a s s hole). I always use lot of lubricant.Initially it is ok but whenever we try to elongate our act it starts paining and increases with time. she says it feels like something is poking her 'there'. One more thing...if i stop thrusting at any point of time she feels discomfort specially at the area explained earlier. any similar cases or suggestions?