This is what worked for my DS2. After a feed, lie baby on his belly across your knees with his head slightly lower than his tummy, and rub his back towards his head. After 30 seconds or so lift baby up so he is upright with his head on your shoulder and continue firmly rubbing upwards. Large burp should follow within a few seconds. If not, repeat until it does.

Also avoid eating chocolate and drinking caffine when BFing as this can worsen colic in some babies. And a few drops of colic relief like infacol can work wonders.