colic problem

Need some advise. Bb is 14 weeks old. Have colic issues. We tried avent natural, she rejected. She accepted pigeon wide neck teat. Her feedings is also quite inconsistent. Can be 60ml every 3 hours or 20ml-30ml every 2 hour. We brought bb to GP for a quick check , doctor says she is alright. We always burp bb on our chest after every feed . Is it the bottles issues? She is on 100% formula.