I don't get into the door 5 mins until Mom needs, wants, can't something. I'm a single Mom to a teenage disabled son, and the caregiver to a disable Mother. She has acute back pain and a pain pump in her back. She just had knee replacement and was in rehab.
Why not check out what resources there are for help? See if she qualifies for someone to come in and help with her care or what about hiring someone to clean or run errands? If the funds are available, why not delegate some duties?
Continuing to feel resentment isn't good for your health. It can cause all kinds of problems in your body. I had that happen to me once. I'd work on finding some help. You are entitled to look forward to coming home and relaxing.
Can your mother still write? Can you ask her to write out a list of what she needs and you'll read it when you're ready to give her that attention (after you eat your meal, tend to your son, shower and change, meditate for an hour, come back from the gym, whatever). She's probably afraid her concerns will get lost among all the other things you have to do, so she's trying to be the squeaky wheel. You probably can't change her demanding attitude at this point, but maybe you can shape her behavior so it's less annoying/draining for you.