Bad work situations are very draining. It's easy to say because I'm not in your position, but if you do nothing about things, nothing is going to change. Perhaps people don't realise that they are giving you tasks you shouldn't be doing or how much work you actually have on your plate. Sometimes, a 'no' with an explanation of why not can work wonders. Open people's eyes. You can't expect things simply to change for the better.
Is there another job you can apply for? If so, apply. If you get the offer and it's better than where you are, you're golden; if not, well, at least people will know that you're less than satisfied with your current situation. Easy for me to say, of course, but I'm applying the tough love here. If your best mate was in your situation, what would you advise her? Or your daughter?