Just another idea in case it's not reflux ... if you can, try a chiropracter. Someone trained to manipulate (in the chiropractic sense) infants can make the world of difference. From memory, your DS had a really fast birth - as did DS3. It might stand to reason that he's got a pain in the neck (or similar). DS3's speedy delivery appears to have had an impact on his cranials and pelvis. After a few weeks of chiropractic care, he's gone from a shocking feeder on my right breast to being pretty good most of the time. The chiro also helped DS3's horrid wind pain (colic) and his mega chucking after a feed.

Good luck - feeding a new-ish baby can be very, very stressful so try not to be too hard on yourself or your bub. xx