I believe my sister is avoiding me.?

Okay so ever since I became pregnant she has avoided me and has just been alienating my folks and I, she already has 2 younger daughters and a older son she is pretty much done with kids. I have a older daughter 2 year old son and I am 26 weeks pregnant she has not mentioned to my mom about participating in my shower so my mom will be the host, I told my mom I didnt need another shower but she insisted so I couldn't argue I fidget rid of all my baby stuff. I got pregnant on bc so this baby was not planned. I just don't know why my sister is being like this she doesn't call me anymore I always have to be the one to call and when I do she is so short all she says is "Yup"....Sure....ahhhh huh, I just can't believe I just want to tell her how she is coming across with me, I invited her, husband and her kids to many events she always says maybe, I'm done it's been a week since I last spoke to her if I don't call she won't call me... I literally think she hates me! She is my only oldest sister I don't understand it's sad really but I hate drama and lets see if she calls me for my birthday in two weeks.