ds is being fed with bottles. the problem is that he is really gulping his milk! i can hear the air going down into his tummy and then he finds it really hard to bring back up, this results in the next 20mins trying to burp him, then we resume the feed and he gulps again! we have tried infacol, which worked for the first two weeks, but no longer seems to help. we also use the dr browns bottles. what can i do???????