Cheers up mate. It can improve for sure. You have to get on the right track. I agree with what you said. Stuttering is also tiring. I believe when we stutter because we block and our words cant get pass our mental wall. When we face this brick we try to make physical effort to get our words pass through. Its is non sense because there is no real wall so no need to make effort. But that is why we get tired. If we can measure our muscle contracture while on blockage im pretty sure that the levels will be superior than on rest. ¿Why we eventually speak? ¿Is it because of the effort? Because we can´t make effort forever, at some point we get tired and the effort wore off. It is then that our muscle relax and the"wall" momentarily dissapear so we can speak. A word of advice: whenever you feel like you are making a physical effort stop right away. Instead try to relax and notice that there is no real wall. It is only fear. Wait patiently until the blockage diminish and then attempt to speak.