Problems with the relationship with my mum?

As I suffer from a chronic illness I can understand her being irritable and snappy because the frustration of not being able to do anything is enormous not to mention living with pain. I do keep a lid on it though and maybe your Mum needs to do this. I suspect she is severely depressed and maybe, if she is willing, she should see the doctor who might be able to help her. If she refuses then maybe you should tell her that you cannot take what she is dishing out anymore and say you are going to move out unless she stops - that may give her the jolt she needs to pick herself up. Good luck and I so hope things work out for you both.