I do get the 'extra phlegm' stuff too, but believe it to be from Bartonella for me. (
www.gordonmedical.com/unravelling-complex-chronic-illness/bartonella-like-organisms-blo-consideration-signs-and-symptoms/)
Right now, I'm dealing with a very stubborn sinus infection though, so I feel your 'pain'! The only thing that I have found helpful when this gets bad is Mucinex, because it has Guaifenesin. This is something I got started using years ago, when I was only diagnosed with Fibro/M.E.