maybe you should find out what's the problem first.
Is it time?
The two of you seldom have the chance to be stay home together, she
always need to OT and come home late?
If the two of you have a lot of time being alone together at home,
but she rather sit there watch TV than to have sex with you, than
the problem is not about "time".
Enviornment?
Are you at the stage that not married, but she stay at house, only
go back her home once in a while? If yes, do you have siblings?
Your parents likes to knock your door every now and then?
You didnt do your part?
Not saying that you sucks in sex, pls dont misunderstand me. Some
girls like it slow, you have to talk to her for a while, hugs +
sweet talk, then starting kissing, then start to "browse" inside
her clothes, then take of her clothes, then some foreplay, then you
can have sex with her...... Dont expect you just say "darling,
let's have sex" and she then said OK and take off her clothes. Some
girls cant accept it. Dont initiate sex by simply saying you want
it.
If she's not in the mood, try to change her mood.
Treat her better, make her loves you more. Play some slow music.
Dim lights. Try possible ways to make her go into romance
mood.