Dementia is undoubtedly a demanding illness for the immediate caregivers. Most of the caregivers have emotional fallout of the burden of care, including 'burnout'. A simple (but difficult to implement) strategy to prevent and alleviate burnout is to give sometime to yourself. You should ask some other person (a relative or a paid help) to manage your mother for the entire day, at least once a week. This should help restore your emotional resilience. If you are unable to feel good even during such break, you should consult a Psychiatrist for treatment.

It is your inability! I think you are irritated because of the fact that you are the only person who has to handle all these responsibilities. I would suggest you to consult a psychologist for a better understanding about yourself and your responsibilities and will be able to handle all those pressures.