Obligation and Resentment

Life is full of obligations. Most of my obligations are self imposed. There is the obligation of being self employed. The obligation of having employees. The obligation of children. I chose all of these obligations. The obligations that I did not choose, but feel I must honor, are the most challenging ones in my life. The challenge is how to balance doing the right thing, with love, and not resenting having to do it. It is easier if the job comes with kudos. Most of the time, doing the right thing comes with silence. I have said for years that it is just "stars in my crown" when I do something unrecognized. I struggle all the time with a certain level of resentment. I guess I am back to that old evil, control.
I resent it when I am doing whatever it is I feel obliged to do and it interferes with what I want to do.  I know that I should just go for the "love and cheerful heart" thing, but when I least expect it, in comes the resentment. I try to be objective and balance my feelings. I often, do the right thing with an even (flat?) attitude and a fake smile. I have been told all of my life, if you want to have a good attitude, fake it, and the attitude will come. That is sometimes true for me. Abraham Lincoln said "You are only as happy as you make up your mind to be." It is my daily goal to make up my mind to be positive and cheerful. 
I have taken care of people all of my life. First as a nurse, then as a sales clerk. It is the same thing. Everyone has an obligation to be nice. You see a need, you try to take care of it. I guess the resentment comes, when nothing works. Since I cannot control anything except my attitude, it is up to me to make the adjustment. In rare situations, I just decide that I am done. The obligations that are "duty" are exempt from that. How do I  take care of whatever needs to be done and keep a good attitude about it?
I know people that are angels. They get up everyday and take care of a loved one and don't complain. I am not one of them. I feel bitchy and prickly when that resentment rises. It does me no good. The obligations do not go away.
Are these the "tests" that we are told we will have? Will I be one of those "duty obligations" for someone someday?
I will try my very hardest not to be, but if life has other ideas, I know that I will remember the battle  I have had with resentment. I know that I will be better.