I have been pumping 8 to 10 times a day since my premie was born at 29weeks to keep my supply up and occasionally I would try to get him to latch but all he would do is scream. Last night I was pumping and he was fussy so I tried to get him to latch an he did. He latched for 20 mins each side. Then he did it 2 more times for shorter periods before he went down for the night. This morning he nursed for 15 mins and acts like he's done and satisfied. I'm new to this. Is he nursing long enough, is he getting enough milk? How can I tell?