It sounds like you're having trouble keeping him awake. I know it's not always possible, but try to feed him as often as you can with him just wearing a diaper. He'll stay awake because he's cold and will want to stay near your body to be warm. Alternatively, when you see him getting sleepy, do a diaper change and put him back on the same breast. You could also break the latch and do some "baby sit-ups," where you lay him down with your arms/hands under his arms (hands supporting the neck and head) and lift his top half up and down to keep him awake -- then have him latch on again.
I'm sure I'm forgetting more tips to keep a sleepy baby awake, but I'll come back and list more once I find my book!
