Hello honeybun
Yep, know the feeling. Irritable is my middle name at the moment, everyone and everything annoys me and I'm constantly angry with myself for being forgetful, tired etc. Someone on this site once described it as PMT times a hundred and I'd agree with that.
As for elderly relatives, my mother-in-law makes constant demands on my sister-in-law and is never grateful, just critical all the time. My husband and others also help a lot, infact she has a small army at her beck and call but it never seems to be enough somehow. It is very hard work so I'm not surprised you are feeling the strain.
No magic answers I'm afraid, just sympathy and understanding.
Wishing you well and take care.
K.