When would you change formulas?

NickyCicc20

LO is extremely gassy.  She's having regular BMs but has a hard time burping and generally looks so uncomfortable.  She's almost always crying when she's up

She's FF and has been on Similac Advance since the hospital.  We're thinking of switching to a Gentle formula (Enfimil Gentlease maybe?) but don't know if it's too soon (she's just over 2 weeks).

We saw a nurse practitioner at our pedi's office earlier in the week and she did not give us the advice to switch but I just hate seeing LO so uncomfortable!  We've managed to get the constipation under control with some prune juice, rectal thermometer, etc.

When would you change and try a new formula?  I know that they get fussy for a week or so after changing but it's just killing DH and I to see her so miserable and we're not sure what else to do!