My stuttering has been a rollercoaster for the last 15 years (I'm 28). Sometimes I would be perfectly fluent for several months, then I'd pause, get blocks, the letters of hard words change, from mild to "fuck-this-shit-I'm-done"... Haven't been able to find anything specific, frankly sometimes under heavy stress my speech would become perfectly fluent and the opposite, being calm, I'd stutter from time to time. What reduced my issues in general and seem to always help significantly is following: 1) Getting good sleep, 2) Breathing coherently and fully, 3) Speaking fewer words on one breath, 4) Looking on the one I'm speaking to.