This is a big issue for couples that are living together. Some will even go days and weeks without touching each other. These reasons are generally the problem.
She thinks it’s all about you. You may think just jumping on her when cuddling on the couch and saying “let’s do it” is romantic but to her it is anything but. Your enthusiasm isn’t in question it’s why you want to do it that is. To her if you always finish before her and never finish the job this will always come up as a reason she won’t give it to you.
Just reassure her and make her pleasure the first and foremost in your mind.
She’s pissed at you. This is an obvious reason why she isn’t willing to do the horizontal mamba with you. Maybe it is as simple as being late for dinner. This may seem very trivial but to her it may stop you from getting any for up to a week. To get you back in her good graces apologize for what upset her, even if you don’t think you were in the wrong this will squash the whole dilemma. Then let her know you want to make it up to her in the bedroom if she will let you past the door.
You’re neglecting your hygiene.
She may love you just the way you are, but the three day old stubble and gym shorts aren’t on that list. Nothing can make her want to get down and dirty with you when you are stinking. So shave, shower and change your clothes daily. Please don’t forget to brush your teeth.
This is always the easiest to spot. She’s just not feeling sexy. On a fat day she will want you as far from her as she can get you. If she has been complaining a lot about her looks the easiest way to fix this is by just taking the hint and being sweet. These might just help you get some more often.