Is my girlfriend cheating on me?

we been going out of almost a year now..she been starting fights with me for no reasons and said we need time off from each other. (plus i didnt really do nothing) she told me she was going to spend the night at her friends house the night before she was gonna go away for 2 days with her aunt and gram. but i ask her to spend the night with me but she starting fights with me again and she said she was suppose to go to jess party and jess was upset that she didnt go. (she didnt even say nothing about a party until that night she only told me she was going to stay over her friends house but the friend wasnt jess) i doint really know but it been like for like 3 weeks already idk what to do