My DS is now over 12 weeks old, but still waking to feed every 2 hours over night. He can manage 3-4 hours during the day, still being demand fed. He never feeds more than a couple of minutes at any time, and if I try to get him to go back on the breast or take expressed milk he refuses. He is staying on his 2nd gentile so I'm not worried about his weight but I am getting frustrated over night- any suggestions?