This means that you haven't been occasionally informing her about tacit "go-aheads" the barista, the waitress, or the lady at the parts counter were giving you on a particular day. Or it just means she is relationally stupid. It exists. Any woman who does this has either lost interest, she's been asexual since day one and feigned interest until you made a deal that's hard to welch on or she just doesn't understand that when you don't do it, men go kookoo and most men can't deal with it. They can't deal because they either don't know how or they're trying to do the "right-honest-faithful" thing.
Any man finding himself in this situation he needs to ask himself HONESTLY about how it became this way. And then he needs to leave the relationship. 99.99999% of the time, setting a REQUIREMENT for sexual frequency is just as damning to a relationship as a woman setting LIMITS for sexual frequency. If it's always planned or scheduled, there's no suspense, no urgency, no thrill, no fun. If you're horny, grab that ass and pull her hair, make sure she 'feels you' and say "You really should have known, wearing that around the house." Or just stare at her from across the room and say "Yeah horny! Yeah-fvcky!" You'd be surprised what little effort it takes to 'get things going' when it's never planned.
If it escalates, great. If it doesn't, you try later. If it never does escalate though, you've got something to discuss and quite possibly something to get away from.