Struggling to get along with my family?

I'm 18 years old. My older sister is 20 and then there's my mom. I honestly feel like they both hate me or something. I've been sitting here crying for the last hour because I feel like my sister has absolutely no consideration for my feelings. She is also extremely difficult to talk to which is why I'd rather get some advice on this then even try resolving things with her. As for my mother, she is no help because all she ever does is side with my older sister. We're going on vacation in a couple of days to a totally different country and I am just not prepared to go anywhere with them. I don't feel like I'm going to have any fun and I just really wish there was a way that everything could be better.