I know exactly how you feel, I have had a stammer all my life. I have learned to hide it well but it puts a great strain on you and people do not understand how much of a disability it is. All you said really resonates with me, I felt I could have done better in my career but certain jobs would be too taxing on my speech to do this. Keep trying that is all I can say, try not to let it stop you living your life to the full, life is tough with this impediment but do t give up, keep going you are a better person than those out there who laugh and reticule people like us.