Your mother has been thru a lot, and may not want to accept what is happening with you. Put all your feelings in a letter to her, when one has to sit down a read these words, they then, hear what you are saying. But you are an adult and should be handling this on your own, she may be just as afraid as you are. So, don't you think it's time to give back to your mom and seek the help you need, to ease her fears? Don't allow fear to paralyze you, instead let it drive you to get help and make a life for yourself.
If you knew how many people are alone in this world, are terrified, but still do what has to be done, you would do it also. You have a choice, you can continue with the miserable life you have or seek help, which will only be scary the first visit, and gets easier with time. Since you have two sisters who are suffering, why not ask one of them to go with you, I know they would understand. If not, you can do this, I know you can. Fear is very easy to conquer by just doing what you're most afraid of. If you want peace of mind, and a life, face your fear and go for help. Just doing this one thing will make you feel less fearful, stronger and more self-confident.
I understand, I talked to my mother about seeing our family doctor. When I talked to her about my problems she pretty much said that what I'm feeling is normal, and that I just need to get up and exercise. I felt at a loss for word, like how can I better explain myself to where she can understand? It doesn't make any sense that she would react that way when my sister has been diagnosed with bipolar disorder, and my other sister has been diagnosed with borderline personality disorder. I'm just very nervous and anxious when I think about going to see a doctor/psychiatrist by myself...
You really need to talk to a professional about this. Although you do have symptoms of depression, we are not doctors and cannot diagnose you. But there is a lot of help for you and speaking with a psychiatrist will help you figure out what is going on, and the best plan of action for you. Know you're not alone in this, many of us have experienced exactly what you are, and we do care and understand. Take that first step and see someone so you can get your life back.
Take care....