Babies under 6 months can have antibiotics, they prescribed the to kurt when he was about 2 weeks old because they thought he had some sort of gastronenteritis because he wasnt keeping his milk down. (turned out he was lactose intolerant)
If Rebecca does have gastronenteritis no matter what milk you give her be it soya or anything else isnt going to make a difference as it will lay on the lining of her stomach. In turn still making her ill.
The only way to clear the system of a baby with gastronenteritis is to starve of all milk but make sure they are still getting plenty of water so they dont dehydrate (and i know how awful it feels to feel like you are starving your baby i went through it with beth) but if you do give her any form of milk it will just start it off again you need to give it enough time to flush everything out of her system.
Once she has been 24hours without being sick/diarohea (sp?) then slowly introduce milk again so that her body can readjust to it again.
If you do think there is a chance that she may be lactose intolerant. There are to things you can try one is SMA Wysoy (which is soya milk) the other is SMA LF (which is lactose free milk) i actually phoned the sma careline last week to find out what the difference was between them, what they told me was the the LF is for babies that are lactose intolerant as it has all the lactose removed from it, and the wysoy is for babies that are allergic to the protein in cows milk.
Both of them are available on prescription all you have to do is ask the gp for it, the sma careline actually advised me not to buy and to get it on prescription from the gp. If you find she is still the same with the LF then it may well be the protein that she is allergic to as a pose to lactose.
I had something called colief suggested to me last week
http://www.pregnancyforum.co.uk/forum/v ... hp?t=10994
basically you add it to either breast milk or normal formula and it helps to break down the lactose in it. The woman i spoke to swears by it - i havent tried it yet so i cant say personally how well it works, but this is also available on prescription too.
With lactose intolerance a lot of it is trial and error but if you dont try you wont know hun.
Hope she feels better soon, and if you want to know anymore give me a shout x