You are going to have to learn to say NO and mean it. It is, in my humble opinion, crazy tat some in our profession get away with doing no extra curricular activty whilst others, because they care are EXPECTED to DO. We dont HAVE to work excess hours but if we do, this has to be moderated with our human life. My humble advice would be to speak to your deputy head and just say you are doing too much extra work. Ask that others be required to assist.