After doing some light research into this it looks like orgasms increase the level of dopamine in the brain, and thus can potentially cause stuttering in some people. On the flip side, to other people orgasms act as a stress reliever and can reduce stuttering. Different people react differently to this. I would say that if this is something that helps you, run with it. For someone like you who's speech is improved from no orgasms, I wonder if a dopamine blocker would have the same effect if taken before an orgasm.