Bec, Jodi's idea is a good one, it could be a food reaction. Perhaps you could try keeping a food diary and seeing if there is a pattern.

Jack has only ever thrown up once (apart from baby spit ups of course) and he wasn't sick at the time either - one morning he woke up with vomit all over him but he never showed any sick signs and didn't throw up again. At the time I put it down to a new food as we had been to a party the night before and he could have eaten something he hadn't eaten before.

Otherwise, I'm sorry I can't help, but I do think it's worth mentioning to the dr.