Why am I angry and upset?

I've been through a lot of challenging things. My real mom has always been closer to my older sister. She remembers my older sisters birthday from me and my younger brother. I didn't find out my birthday till I was older and found it out from my step mom.
I decided to stop talking to her and have noticed/gotten this feeling my mom and my older sister talk all the time and that my mom doesn't seem to care about me or my younger brother as much. It really bothers me and gets too me.
I recently got in contact with my older sister only to find out that she is more like my mom. I'm not sure why I'm filled with so much rage. I remember telling my mom my story and her just not really believing it. One of those things like I wasn't there I don't know and I prefer to stay out of it and uninvolved.
I blame myself a lot and think I'm the problem and am the reason we don't have a good relationship. She doesn't seem to really care about me. When we did talk it was always about other people. I found out that she doesn't want to be involved with my younger brother which pissed me off cause he's getting abused. She doesn't seem to want to be involved with me either. She doesn't seem to care much. I keep thinking it's because of me and the fact I decided to speak up about my bratty half sister and about my younger brother and her choosing to not be involved. I finally stopped talking to her. But I feel so angry. When i went to talk to my older sister I just got this feeling that my mom would never love and care for me the way she does my older sister. Along with the fact that my older sister is like my mom she doesn't seem to be concerned.
Why am I angry and upset?
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