How can i communicate with my girl who doesnt talk much?

i'm dating this girl rite, but everything seems to be going downhill.. we were so in love... and we stil are despite the fact that we got back together 4 days ago. but from ever since there has been this awkwardness when ever we're on the phone talking. it's like all our communications has become lame n boring. she's always silent and it frustrates me. but on the other hand she says that i'm not talking to her. the thing is, when i do talk to her, her answers varies she always say, ';i dont kno'; ';i dont want to talk about it'; or she jus says ';nothing';. it is really getting to me, because i need her to be happy at all times. when she's ';upset'; with me she say she doesnt wanna talk to me or she hates me.. when i ask what did i do she says ';nth'; so i jus let it be an dthen a few mins later she txt me saying tht she's sorry. she's always apologising. i'm trying really hard to communicate with her but its jus not working. its really hard to please her. i know she's in love with me and so am i. but... its really hard. sometimes i wonder if i'm doing something or saying wrong. this is the first time something lke this has happened. i can go on for hours with ma previous ex altho they didnt last long.. i keep on wondering what is so different with this girl... I NEED HELP!!!! ASAP!!