Refusing to nurse at 9mo

Casey

My 9 month old boy is starting to refuse the breast. He gets very angry and frustrated when I try to get him to nurse most times. He arches his back, cries, rolls the opposite direction; he never did these things until recently. The only time of day he willingly latches on is first thing in the morning. I know I have milk because his sister nurses happily still, but he wants nothing to do with me all day. He takes sippy cups with water and formula very well when he's with his dad or my mother. Just don't know what to do or what's going on, I so wanted to at least make it a full year but I'm afraid now that it won't happen.