18, Sad and Hopeless

I am 18 years old and have had these "feelings" for as long as i can remember. I go through these periods (lasting a few days) where i cry, feel so sad and hopeless, and even have thoughts of suicide. It's been happening for years now. I've tried to talk to my mother about my emptiness but she turned around and blamed me for it. I tried to kill myself once by slitting my wrists but i couldn't go all the way. I told my grandmother about it and she just said "yah right, whatever". So basically i have given up talking to anyone about my feelings. I just don't feel like going through life anymore sometimes. No one listens to me or understands so i have to keep everything to myself and its just getting so unbearable. I cry all the time!! I don't even know why half of the time, i just feel so sad. I hate myself. I just cant do anything right or make anyone happy. Sometimes i feel like I'm split in two. A part of me wants help and wants to be happy....But that other part of me always kicks in and wants to give up and i just don't know what to do anymore. I cant control my temper either. Ill be perfectly fine one minute and when someone says something that even slightly irritates me i feel so angry and i yell. When this happens, somewhere deep inside i feel so angry and hateful and then i start to cry cause the pain is too much, but there is another part of me that doesn't know why i get so angry so quickly; that doesn't know why i lash out; and doesn't understand why i cry. Its an uncontrollable feeling. When it happens i don't even realize it until its over. I went through a period where i would be get so angry that i would just blank out, and i had couldn't control it. I couldn't think or even speak for that matter. Every day i feel so stressed about my life. I hate waking up knowing that i have so much to worry about. Other people think the things i worry about are stupid and that i shouldn't feel sad or angry or worried about them. But i feel these things deeper than i can even describe. So deep that it hurts to think and feel anything. Sometimes i get so worried that i get a really bad stomach ache (this has also been happening for years). With all this said, I'm just wanting to know if there is possibly something wrong with me or is it all in my head? Please help me to understand all this, cause no one else will.