I have those days alot too, especially when I am not busy at work or sometimes when I am alone in my thoughts and feel that everyone depends on me. I know most of it has to do with myself when I take on alot. The other day, I went to an event with one of my older sister's, who had been sick, to get her out of the house. Her daughter and a niece went with us. Well we all ended up winning door prizes, even though I didn't plan on winning anything. My concern was to get her out of the house, and showing her a good time.
Fortunately for me, I am not feeling like I could just burst out and cry today, even though I feel like it. I miss a very good friend, and there is nothing I can do about it. We don't talk anymore.
My advice is do something good for yourself. I know it's hard, but it works. Today, I am going to try and get a spa appointment for a massage. I got a half price coupon some months back. Treat yourself to your favorite food or dessert. Do something for you. I sometimes feel that it is wrong to be selfish, but it's not. Remember to do something for you.
Good luck and don't worry, you will feel better.