Would your doctor be willing to give a full blood work-up? If not, do you have another doctor you can do to for this? Once you have ruled out all possibilities of something serious, then you could approach this yourself YKWIM?
Some foods create more mucous than others, so you may want to share what kinds of food in his diet that he's eating so some of the mamas here can speak from experience.
As for tired, it definitely sounds like something is going on, but I don't want to make suggestions until anything serious is ruled out.
keep us posted,