Morgan started at about 4-5 weeks old, and although she wasn't overly sick (not as much as some of the poor babes on here) she would scream in abject agony and be a bit sick about an hour or two after every feed. We knew it wasn't colic as she had that at 2 weeks old, and after we changed to Dr Browns bottles it disappeared... besides, the way she cried was so totally different!
GP said it was an ACID reflux, not just milk being brought up, which is why she was in so much pain, and prescribed Infant Gaviscon. (You can buy it over the counter though, it's about £4.50 for a box of 30 doses).
It made a massive difference to her, and seemed to take the pain away almost instantly. She's still on it now, although we are trying every so often to wean her off it, but she's not ready for it to stop yet, so she's on half the recommended dose at the moment.
Do you think your LO may have it then? I would say that reflux can appear differently... some seem to bring up a whole bottle but not seem too bothered by it... others, like Morgan, don't vomit as much but are in agony with it?