Don't be sorry @outlander - it's good to get it off your chest. Sounds like you are under much pressure and not given any slack. No one is perfect all the time.....I love my daughter - but you are far more responsible than her with bills - even if a bit late. I don't mind helping her out - as long as she makes a genuine effort to pay her share (which isn't much believe me). And to me that's what should matter in your situation, that you make your best effort which you are. That's reasonable - don't feel you are not good enough if others "are being unreasonable" - which it sounds like they are. See it that way, not that you fall short.
Don't see yourself as not good enough - see it "that they are asking too much and not giving you a break". Same with the housework - when there is a physical injury we naturally slow down and can't do what we normally would do.
Give yourself a break my friend and know that by doing your best that you are good enough. It's hard I know when others are making you feel bad - but try and brush it off and not let it rattle you. Unfortunately you are in a position of less power in the family - and that will make you more vulnerable to how those around you treat you. Even though it's hard "always stand up for yourself". Always stand for what is right if you are being wronged.
When your family makes you feel,not good enough when you give it your best shot - take your power back. Don't allow bad thoughts of yourself - talk back to those thoughts with a will and determination and acknowledge your good intentions and strengths (give them the thumb respectfully in your head). And calmly tell them you are doing all you can and you can do no more. Keep a positive vision set firmly in your mind that this won't be forever - that one day you will be treated better. And see what goals and ways you can make this happen. It may be a small step like becoming more involved in other things outside the house that will take your mind off how you are treated - a small step that can lead to better experiences and better things for you. It takes time but worth the effort. Stand tall - I feel your inner strength, it's there - believe in you xxxxx