3wk old Soy FF really runny yellow stool?

My 3week old DD is EFF Soy Similac Isomil (due to pediatrician saying she was lactose intolerant due to regurgitation and major loss of weight on milk based formula after hospital discharge).  She has been on the soy formula for about a week and a half now.  She has been gaining weight consitently and not regurgitating anymore since switching to the soy formula, but for the past 3 days she has had really runny stools, and the colour went from peanut butter colour and consistency, to now being a runny mustard colour and consistency and having a bowel movement at almost every feeding (sometimes twice per feeding).

 It is so runny, it looks like liquid dye in her diaper, and sometimes if she passes gas, she ends up with the liquidy stool all up her back.

 Normally, FF babies have peanut butter type stool,  does the soy formula cause stools to look more like a breastfed baby?  Also, I am wondering if the really runny stool is normal?  Is it just her digestive system developing and getting used to the soy formula?  She isn't dehydrated, doesn't have a fever and is having normal wet diapers, so I don't think she has an infection to cause it to be diarrhea.

Any input would be appreciated!