Resurrecting this thread for the following context (as we were still unsure of what comes next depending on the context )
"Je suis encore amere de devoir travailler le jour de mon anniversaire."
"I am still bitter about having to work on the day of my birthday."
I agree with Pieanne, I wouldn't say 'amère' when describing feelings, I'd rather say in colloquial speech 'je ne digère pas de devoir travailler aujourd'hui', or 'notre dispute me reste en travers de la gorge'.
Hope it helps.