I doubt anything is wrong with you! He obviously married you for a reason (:
The best thing to do would be to try to discuss this with him. Try "I really want to go down on you, but want to make sure it's amazing for you. Feel free to give me directions!" or look up some new sexual positions and suggest that you try them, like "Babe, I really wanted to try *this* - it looks awesome!" This way, you're bringing it up in a fun and sexy way. Who could not want to get it on at that point?
I'm not married so I can't say from personal experience, but from what I've heard from friends, sometimes the spark starts to dim and you have to invent new ways to get it burning at max potential.
You mentioned that he'd rather "jerk off and lie about it" -- did you catch him doing this and discuss it with him? Maybe he said he wasn't in the mood to have sex with you for scolding him for masturbating? If he's lying to you, I suggest doing something to work on your communication. Not an easy task, but once you two are more comfortable discussing things, he'll 1.) Have no reason to lie and 2.) Open up about what the true reason for him not wanting to have sex is because only he knows for sure.
On the other hand, he could simply be stressed out by other things.
Personally, when I'm in "raging b*tch" mode, I tell my man that I'm not in the mood. He understands that this is because I feel like if I can't focus all of my attention on 'the act' (if I'm caught up thinking about school, work, bills, etc.), I'd rather not do it at all. Maybe he feels the same?
Many other factors come into play -- age, the amount of sleep he's getting, the mood he was in when you brought up sex...
I wish you the best of luck! Keep us updated (: