@Michael – your question in regards to not being able to flutter.
My guess is you’ve already read how to do it? and you’ve spent considerable time watching youtube videos of people showing how to do it?
I think the best thing in your case is to get your sax teacher to show you how its done.
I maybe be conpketely wrong but in my oppinion i think you may have hearing problems, just based on your comments that you can’t hear the sound difference between different mouthpieces used by the ssme players?