Why does my sister not bother with me anymore?? or her niece?

My sis is 19, i am 23 and my daughter is two. Me and my sister are both due to have babies v. soon. My sis has literally moved around the corner from me with her boyfriend. but she never bothers to meet up go shopping, see her niece or anything. she don't bother going round my mum and dads either. but she is happy to spend all day round her boyfriends mums house. She didn't even bother getting me a card for my birthday. and whenever I phone her she can't be bothered to come round or go out. she don't seem to bother much with her friends either. she seems attached to the hip of her dosser boyfriend. I don't understand why she don't wanna see me or she arranges and blows me out with a stupid excuse. I know she ain't got a problem with me or our mum and dad. And i'm so pissed off as were a close family, and all like to keep in touch. why is she being like this?