I've also found my band is very inconsistent. I've realized lately that a big issue that no one really told me about was dealing with my allergies and sinus drainage. It seems like when I have a lot of sinus drainage, my stomach is really irritated and I have problems keeping most things down, but if I remember to stay on top of the decongestants and allergy meds, not only does my head feel better, I'm able to eat more consistently.
I asked my doctor about this and she said it is very normal, but haven't really seen too many other people comment on this issue. Now is my peak allergy season and it just seems like my band hates the pollen as much as my head.
Oh well, this will pass . . . soon, I hope.