At this age, he should be eating every 4 hours during the day, and not at all during the night (since you say he is a big baby now, and not underweight). I think the problem is that he is "snacking" and not eating big, full meals. This means he is not getting the richer hindmilk, and you are becoming exhausted. I think what you need to do is feed him at 6am, 10am, 2pm, and 6pm. Burp him, change his diaper, and put him to bed shortly after 6pm. Yes, I know it sounds ridiculous, but just go with me on this. If you hear him waking up at night... just let him be. He may fuss a bit, but don't go to him unless you hear him really wailing. More often than not, babies are just going through a period of light sleep, and by picking them up, you're waking them and making the situation worse. So... rustling around in his crib = just leave him there for a bit and see what happens. He might go back to sleep.
Now, it's possible he may be truly hungry at some point during the night. As long as it's after 10pm, go ahead and feed him. Really make sure he eats a good meal. Maybe change his diaper once he's eaten on one side, before he eats on the other side. Don't let him fall back asleep until you're sure he has eaten his fill. Burp him and put him back down. I would imagine that once you get him off of "snacking," he will get into a great sleep pattern and will be fully sleeping through the night in a week or two.
I read the book "On Becoming Babywise" by Gary Ezzo, and it goes into more detail on this. I really found that book to be invaluable when it came to getting my kids to sleep well at night.
I hope that helps! Sweet dreams!