I wasn't going to post on here again but have been lurking a bit, and couldn't resist posting to help out when I saw your post Lunavix.
I am an expert at gastroenteritis. Dd had it about 6 / 7 times when aged between 6 months and 15 months and ds has had it about 4 times already (on the last but one occasion requiring hospitalisation for dehydration). The reason for all this gastronenteritis is that they attend a Day Nursery on a hospital site, and the clinical staff bring all the bugs with them when they go to collect their children. Unfortunately we've always got clostridium difficile or norwalk virus on the wards.
I can't remember if you are breast or bottlefeeding, but if the latter the best way to knock the bug on the head is to avoid formula milk for at least 24 hours. It really does feed the bug. When ds was hospitalised last time (after 5 days of vomiting)I had unwittingly made him worse by persisting with his formula milk even though he was vomiting it up consistently.
He recently fell ill again (vomited last Wednesday), I withdrew milk and he had perked up by Friday. I tend to give diarolyte mixed with fruit cordial (to make it more palatable) from a formula bottle during this period. Makes us look like chavs but never mind. He won't take diarolyte or water from a beaker except in small sips and becomes frustrated, whereas he considers a bottle of diarolyte to be a proper substitute for his milk.
One more point - they can suffer temporary lactose intolerance after a GI bug. Ds is in that situation now, although fully recovered from the bug he can't tolerate milk which immediately makes him sick, and yet he tucks into 3 hearty meals a day. Temporary lactose intolerance is a fairly common side effect of a GI bug and lasts for up to a week after the bug has got better. Basically the bug causes short term problems in the gut affecting the enzyme which helps with digesting lactose in milk...(at least having researched it a bit, I think thats what happens)
In short, avoid milk...