Lucy,
You are allowed to take a break once in a while from all the worrying and focus on your brother and nephew, sweetie. You are a working, single mom, which is tough enough without all the added stress. Try to step back for a day or two and have some Lucy-time... all the problems will still be there when you are done. This may mean giving yourself a no-answering-the-phone for a day or two, taking your own children out for a meal and some fun, or asking someone to babysit for YOU for a change so that you can have some down time. Remember, if you aren't at full strength in taking care of yourself first, then it's doubtful you can be there for others. Hang in there!