I appreciate you writing us here at PsychCentral. I think we want to approach this from three perspectives. First, I think it is important for you to get treatment for your depression. It is time to find a therapist and the Find Help tab at the top of the page can help you do so. You can also call the local hospital to find the nearest clinic. They have help on a sliding scale if you do not have insurance. Along these same lines you can join the PsychCentral Forums. They can help as both a resource and support.
Secondly, from a practical point of view, the fact that you are staying at home watching your little sister is likely at the core of the problem. At 27 you are stuck in your family system and need to be given an opportunity to grow. I would find ways to unhook yourself from the full time job of supporting your mother’s job. There may be friends, relatives, or a cooperative group of parents that could help. You need time to be out getting your own job or going to school.
Finally, it sounds like it is time for you to develop new friendships, meet new people and start having goals out in the world. Your new therapist should be able to help in this regard, but I wouldn’t wait. Start looking for ways to change your daily and weekly pattern by getting out with others.