Hi, I'd like to help you with your question.
There are a few reasons I can think of that might be the cause of your problem staying on task.
Are you choosing activities based on interest, or are these tasks you feel you must complete? Your level of interest and the reasons you chose a task can affect how you complete what you started. For example, someone may be asked to plan a party, but if they tend to be non social in personality, the task might be easy to start but very difficult to finish. Since you mentioned being a loner, this might fit for you. Some folks are just not interested in doing much activity wise, and that is fine.
You could also be exhausted from caring for your mother. You may not notice the symptoms of being overtired. Being unable to focus on tasks would occur if you were burned out and haven't had sufficient rest to recouperate your strength.
Another reason might be that you have symptoms of ADD/ADHD. With a very mild form of this diagnosis, you could experience inability to stay on task. A common ADD/ADHD symptom is trouble staying on task. Some other symptoms include:
In order to find out if you have ADD/ADHD, contact your doctor for a referral or go on line to CHADD.com to find a specialist in your area. You need to be tested to be sure you have this diagnosis. You can also take tests on line, though they are not as accurate as a face to face evaluation. Some sites on line include Psychcentral and ADD.com.
If you do end up with a diagnosis of ADD/ADHD, there is good treatment out there to help you. Talk therapy is very helpful, in particular cognitive behavioral therapy. You can also help yourself by making sure you get plenty of rest, exercise, and eating well. You mentioned caring for your mom so you may need to set up extra help so you can take time for yourself. You need to care for yourself so you can be there for your mom. Even without the diagnosis, this would be a good idea.
I hope this has helped you,