@TheJames101 is so right... She might be just tired. But she might also be stressed, preoccupied by something, bored or no more interested toward sex or toward you. Only you can say. Ask her and listen! Is it a new situation? Women libido is also link to female hormones, menopause. Maybe she has health problem, her doctor could help if she wishes. Does she get orgasm? Some have no idea what it is. They like caresses but do not know about the real thing. Women and men are so different. It's wonderful but it brings difficulties to understand each other.
I had a girl friend with a stressful job. From Friday night to Sunday morning it was open bar. And the bar was always full in quantity, diversity and quality...
Same thing during long week-end and vacations (she had 2 months by year). Sex was never a problem for us.