Mucinex (guaifenesin alone) shouldn't make you tired. It thins mucus, but from my expeience it doesn't dry you up. I have taken it for 40 years because I have always had thick sticky mucus that contributed to chroonic ear and sinus infections.

When you buy Mucinex, you need to get the MucinexER (extended release), not MucinexDM or their other formulations with added ingredients.

Have you tried Mucinex?

Seconding what @sueinmn said about mucinex. Between inhaled hypertonic saline and mucinex it increases the volume of gunk making it easier to huff out. I take it daily and have not noticed fatigue. Your experience might be different as bronchiectasis is heterogeneous (varied and diverse) but it's worth a try.