While I am not a caregiver for anyone, I am a hospice volunteer and so have contact with the families and caregivers on a daily basis. I can see when the caregivers are starting to feel the pressure of the demands of their situation and I step in and do what I can.
The most important advice I can offer is to allow yourself to have a break from the situation, even if only a few hours. Hire a sitter to come, or if money is tight, perhaps ask a friend or neighbor if they would come sit. Even something as simple as getting a change of scenery, treating yourself to a mani/pedi, makes such a world of difference in your outlook. And DO NOT FEEL GUILTY for getting overwhelmed with the situation. It is a demanding job physically and emotionally, and the best thing you can do is take care of yourself first and foremost. If you don't, you won't be any good to anybody!