My DS2 was a happy chucker too. It lasted the whole BF journey (mine was only 10mths). It continued onto the next stage as well. It had no effect on his development or weight and I didn't have feed him again after he threw up. Like your DS he was never stressed or in pain...he just threw up alot. I had heaps of those old fashioned cloth nappies (the one's you have to fold yourself) and used those as chuck rags.
He did end up having a dairy intolerance, not sure if it was related or not and now after years, I am still not 100% it was as he has been diagnosed recently with something new, he is now 5yrs old.
We went through the whole allergy testing, and it was inconclusive on dairy, we were advised to stop it anyway and re-introduce again 6-12mths down the track. We did and he was fine.
Worth a chat to the MCHN, it could also be a little reflux. The Paediatric Gastroenterologist we saw with DS2 thought that maybe he had severe reflux as a baby, again it wasn't something ever diagnosed as he was never in pain and ever under weight.