Please, mama, don't quit! he's only 4 months old. If he's waking it's because he needs it. Sure, plenty of people say their kids STTN at this age and earlier. And some do. But I truly don't believe the majority of kids do. And certainly not breastfed infants. Many experts agree that breastfed infants don't sleep through the night until much later. And honestly, nursing in the night is more than just NOURISHMENT, it's NURTURING. It's necessary. Also, at 4 months old, breastfed infants really start noticing the world around them, so they're more distractible and take in less calories during the day. THey make up for it at night. This happened with both of mine, and I was so relieved to read this article: http://kellymom.com/parenting/sleep/4mo-sleep.html In fact, this is a great page to read about sleeping and the breastfed infant. http://kellymom.com/parenting/sleep/sleep.html It even has a section on "normal" sleep habits for infants. Remember that a lot of people's experiences are based on formula fed infants, ESPECIALLY PEDIATRICIANS. Even the growth charts that pedis use are based on statistics of formula fed infants. BReastfed infants have different needs. If you are dedicated to breastfeeding, remember that your child's demands will tell you what he needs, even if it's just comfort - but even comfort nursing helps maintain your supply.
Please don't listen to the well-meaning people who "think he should be sleeping through the night". They are not his parents....you and your DH are. Everyone I know that has nursed their baby on demand (as breastfeeding experts suggest) do not have babies that STTN at 3, 4, 5 months old. If it is not negatively affecting your life, why change what he is telling you he needs? My son was also 15+ lbs at 4 months old, and he NEEDED to eat, believe me. And why give him nutritionally inferior cereal or solids (like some people will tell you to do) when a) they are not as good for him and b) it is believed by many to be a MYTH that solids or formula will help him sleep longer. http://kellymom.com/nutrition/solids/solids-sleep.html But remember that breastmilk is digested differently and perfectly. Well-meaning people (including your pedi!) may suggest giving cereal at this age because he is "old enough" but there are many (including the American Academy of Pediatrics and the World Health Organization) that believe no solids should be given before 6 months in order to allow baby's digestive system to be mature enough. In fact, they say that breastmilk is enough nutrition for the first 12 months (though you would want to give solids at some point for practice, it's not really for nutrition!).
You're doing a great job, mama, and if he's happy and you're happy, then that is what matters. Don't listen to people that tell you what he "should" be doing: all babies are different and what you should be doing is what he is telling you he needs! Good luck. You are doing right by him by continuing this way.