My life is falling apart... Please help me?! please?

My life is pain.... Since i entered kindergarten am always being bullied and now this girl who bullied me since 4th grade is still bullying me and she wont stop. Everybody hates me. I dont no why? cause whenever i have a friends i always find them talking behind my back. I am not ping 9th grade. My parents, sister and me live with the wife of my uncle and she treats us like trash. Her son is always hitting my sister and she wont do anything. I think she gets glad. She hates us and enjoys making our lifes like hell :( My dad has diabetes. And recently my sister(3 yrs) has being diagnosed type 1 diabetes and I cant take this anymore... I have a feeling inside me every time she has to take her insulin shots and check her blood sugar 5 times a day. How i wish my life could be different. I dont get why i have to be living with pain and sadness. Am always worried most of all because my sister and dad. My sister is only 3 years old. she is too young to have diabetes. I wish god couldnt never give me all this pain am feeling, Too many things going in my head i wish i could die!! I cant take this anymore.... What should i do?? Help me please!