Advice Anyone ?

my girlfriend and i have been together for almost 6 long years. but we have been a bit on and off . so now we started back again a couple months ago . when she got me back she was happy excited you know . then all of sudden her moods changes with me . she shows me no affection really , don’t like it when i kiss on her and stuff . can it be because she tired from working all week or maybe it’s someone else ?