Z.L.
It sounds like he was light weight to start with. What does your pediatrician say about his weight? In my experience the need to self sooth with sucking is still strong at this age. Try only letting him use the pacifier at nap/sleep times. Give him plenty of time to nurse and don't let him fall asleep nursing. Keep him up until he's gotten his 40 min (or what your ped. recommends) of nursing in or if you're using bottles you might want to use them to measure out the milk so you know how much he's getting. I found using the EASY (Eat, Activity, Sleep, You time) system worked well to start. But I also found that sometimes my daughter was just plain hungry sooner than I had planned to feed her but I let her set the schedule since I had no way to know exactly how much milk she was getting nursing.
Hope this helps.