First of all, don't feel as though you need to just "survive" or live with this problem thinking that it's nothing because your sister's are having problems too. Also think that maybe your parents are over-stressed with all the health problems in the family that they cannot keep up with everyone.
Do you ever go shopping with your mom? I find that is the best time to talk to my mom about something. When its just me and her in the car, or we're out at the store. Maybe just ask your mom if you can go to a therapist, or get some medication. Or maybe you are depressed because you feel left out. Would it make you feel better if your parents took just YOU to a baseball game or something? If it would, maybe you should tell your parents that you don't feel close to them and you have a hard time telling them things, and that you wish you could spend more quality time with them.
Anyways, just some suggestions!
I hope you get better!
Quitters always lose, and winners never give up.