2w old girl fussy and gassy breastfed/supplemented. pediatrician changed to soy formula. normal bowel movements only during rectal stimulation worried?

Don't worry: First, if at all possible to just breast feed and not supplement formula at all would be best for fussy/gassy infant. Human milk is for human babies. You'll make enough if she feeds from you regularly. Next, it's ok to do rectal stimulation for a little while if that how she can relax her sphincter. MANY babies squeeze their sphincters instead of relaxing it, and then grunt and cry. Normal!

Pooping issues: Some breast fed babies may have infrequent bowel movements. Other possible cause is cow's milk protein intolerance and of those up to 40%-50% may also be sensitive to soy protein. Do you have to supplement with formula? If so, try a hydrolyzed(broken down) cow's milk formula such as Alimentum or Nutramigen. It is very rare to have a "true lactose intolerance" so do not waste money on lactose-free