Advice please

Hi, I have just applied for pip. I suffer severe copd and emphysema which makes me very tired and breathless most of the time. I also suffer from contact dermatitis and am allergic to many products that make my hands flare up, causing blisters and bleeding. At the moment I work self employed as a massage therapist in a nursing home, I have been there for 5 years and I can choose when and how often I work, mainly 16 plus hours a week. I can’t afford to stop working as my wages pay for my rent and living expenses, but I don’t know how to express myself on the forms. Working tires me out after a few hours and sometimes I can’t work because of my hands, but I only claim working tax credits £3.60 per week, so not sure what to put on forms...thank you