It is hard to give you a definitive answer to this question without more information, however I can give you some things to consider. It may be the caretaking is
wearing you down, and if the person you are assisting goes to sleep or has less needs after the sun goes down, it may be you are finally able to relax and feel free and energized. Another thing to consider is whether your energy correlates with the severity of your fibromyalgia pain. It may be either the caretaking tasks or other tasks are exacerbating your pain during the day. I would also suggest you carefully look over the times you take any medications, whether for your fibromyalgia, depression or something else. The fatigue may be a side effect of the medication. Other questions you may want to consider include: Are there other people around at night to assist you and therefore to decrease your responsibilities? Are you eating healthy during the day? Do you exercise and when? Is there something else stressful going on during the days? Finally, it may have to do with diurnal endocrine changes, perhaps related to your depression. While it is more common with depression for symptoms to be more severe in the morning, there are some people who have just the reverse. I would suggest you discuss your symptoms and these various issues with your physicians. If you are not currently working with a psychiatrist, given these complicated issues, that may be something to consider.