hi, i have a 1.5 month old son.  he was first on hypoallergenic formula but stool was hard, so doctor changed to soy-based.  after 2 weeks, we noticed some threadlike blood (very minimal-one or 2 small only) happened thrice, and oily stools.  Doc changed back to cows milk hypoallergenic but different brand (similac hw).  Now 2 days, no more traces of blood but still oily and watery?  is there anything wrong?
It might be prudent to wait for at least a week before worrying on persisting stool symptoms after changing the milk formula as you have done. If the problem continues beyond a week, you should revisit his doctor.