Sounds like your parent has dementia. Dementia plays havoc with people's personalities and emotions, and often makes them unpleasant and difficult to help.
I'm a caregiver for both my parents, and caregiving is draining. At times it feels the life is being sucked out of me. Another problem (huge) is that the caregiving generally falls on the lap of only one person, at least it does here in the U.S. Caregiving is easier when many family members are involved, when the person needing help lives in a large home with many other family members, and so on. That's usually not possible in the U.S. where the culture is not one of family members staying in the same town or city, but, rather, moving far away from family.
Try to get some help from friends or govt programs. That helps a little bit. Doesn't improve things fully, but that's the way it is here. Also, get counseling for yourself, and exercise. Both of these helped me with the huge burden I have.