There is a lot of debate out on soy products...
Some will say that soy milk is 'bad' because of the phyto-oestrogens in it (they think it will raise oestrogen and make fat loss harder as many blame oestrogen for female fat... but in honesty oestrogen is not the bad hormone for females - it is largely progesterone..)... anyway - for most, soy oestrogens are so weak that they are not an issue - and in some people, they can also act as ANTI - oestrogen as they will block the bodies stronger, natural oestrogen and prevent it from working...
There is also debate about the safety of soy in regards to thyroid health and a few other issues... But the evidence for this is still not clear cut either.
If the milk is fermented soy then the above things are not issues and it will be fine. If the milk is not fermented then you can use it if you want - a weeks worth is not going to do you any harm... (I would not use it PWO (too slow on the uptake) - but you could use it at other times without a problem).
Oh - but it will also depend on if there are any other ingredients - if it lists things like sugar etc as well as the soy milk then I would not drink it.