I find it very hard to hold down a job?

I have a condition and get very nervous if the supervisors explain things to me, trying to take it all in, try and really hope I don't make mistakes. I ask lots of questions to make sure I am doing it properly and can't relax. I either try too hard to go fast and mess it up or take it so slowly they are losing out on time. Not because I am slack but because I want to do it properly. I put more than 100 % into what I do, write lists, write a learning plan myself and work out what I want to learn. I take more effort than most people do, make an effort to look nice, get to work early and give a fair day's work, yet find it hard to take initiative too. Sure I try but then can't think of what else to do and do everything I have to and more, yet bosses say I need to take more initiative in my daily tasks. Some employers say I am wasting their times, I forget little things and get flustered and can't seem to last more than a week, despite my efforts, some say I am too slow and there are too many issues with me, and some employers walk all over me and treat me like **** and say how hopeless I am. I try to attempt a task and do my best but at times make huge mistakes that they have meetings about me, and tell me how hopeless I am. I want to work and know that having a mental illness is no excuse not to work, yet if I don't tell them, they give me a job and don't give me much of a chance to stick with it, sacking me in a week, if I do tell them about my illness, they won't even give me a chance at all. I am stuck between a rock and a hard place. I have a regular income which isn't much to live on, I want to work and have tried hard, yet am so sick of the stress it causes myself and others. I feel so lazy not working and people say this to me too, yet they don't really understand.