HELP! My 3-week-old won't sleep at night unless I hold him and wants to nurse non-stop!?

Why don't you pump in the afternoon before his 8 pm feeding time? Next suggestion, get him in a routine. Feed him, give him a bath, and then rock him to sleep. He is only 3 weeks give him time, at 4 to 6 weeks introduce just a little cereal. If he was a big baby like mine, it is ok to start early, if he is little give him a couple more weeks.