If the days are repetitive then try doing something to break the monotony! Sports, art, walking around the neighborhood every once in a while, volunteering, etc. There are loads of things you can do cheaply and on your own or with others. Might even make a few friends while you're at it.
I'm sorry about your parents, but it's not your fault and you are NOT a liability. It sounds like it's a rough time for everyone, but that's what families are for: to make it through together. I might suggest easing a bit of their burden by showing them that you can take care of yourself. Make your own food, help around the house without them having to ask you, etc.