Does he bring any up later on between feeds or is it only just after when you burp him? If only after.. then its just coming up with the wind. If its later on and he looks to be in a bit of pain (eyes may water or go red) then it may be reflux.
DS was a big puker.. but was fine after about 1/2 an hour after his feed.
Whereas DD is a puker, but also would continue to bring up milk/saliva up until her next feed (and large amounts of it). She was also in pain when she brought it up.. would grizzle and her eyes would water and go red. She was then diagnosed with reflux and is on AR formula. But if this is also the case with you, your GP can prescribe some meds for reflux while breastfeeding.

Hope this helps.