Why does my sister hate me?

My sister is always mad at me and she never talks to me. I feel like I'm depressed and the only reason I can think of is her. Today I took a nap and I woke up to her screaming at me calling me useless, stupid and a burden. Seconds later she calls my other sister awesome and continued to converse with her but everytime I try to talk to her she shouts a mean thing. Im 12 years old and my sister is 18 I don't know if I'm overreacting or not but both of my sisters say I am. I've tried talking to my parents and they talked to her but she hasn't stopped. I can't help but feel she hates me. And I guess Im asking what I should do about it.