Has he always done this? My DD did the same, and it was suggested that i had an oversupply of milk so adopted a strategy of single side feeding which has dramatically helped. It's also known as lactose overload (NOT intolerance).

So i feed on one breast for a 3 hour period and then switch to the other breast after 3 hours (rather than offering both breasts in the feed). This means the breast gets drained a lot better and she gets more of the slower digested fattier milk. It has made a massive difference for us.