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.