Sorry you're having such problems. I think many relationships have a real mis-match of sexual desire between partners - often with the man being way more up for it than the woman.
Are you taking anti-depressants at the moment? They can definitely dampen sex drive, and can make many people unable to reach orgasm.
Do you know why you might have such a low libido? Is there a history of abuse (obviously you don't have to answer this!).
Also, I'm sure you already know that one of the main symptoms of depression is low sex drive? So perhaps concentrating on treating your depression first will lead to a change in the bedroom - obviously 'biting the bullet' isn't an approach that's worked for you in the past.
I am talking from experience - for two years after having my DS I didn't want sex at all. I made myself do it about once a month. But my DH was always 'after it' and I felt pressured by him to have sex, not in a bad way, but just because his sex drive was fine. I felt, like you, that it was another 'chore' to do and often right at the end of the day, when all I wanted to do was collapse in a heap.
The expectation that sex would happen e.g. if we went away, or someone has DS for a night, really really completely turned me off.
What has helped for me has been therapy. I've been going once a week since May. (I am paying £30 a session, which I really can't afford, and am actually going in to debt for, but I just had to do it). We haven't even really talked about sex much yet, but the effect on my mood has been significant. It's hard to put a finger on exactly what has helped me but it's definitely working. Working so well, in fact, that I had to invest in a vibrator! We're not exactly at it like rabbits now, but I'm enjoying sex a lot more and have had the pleasure of initiating it a few times. For the first time in my life I can actually see what all the fuss about oral sex is about too - miracle! I also invested in some erotic literature to try to stimulate my imagination a bit.
That's the other thing, I guess - never having the thrill of seeking sex out. I don't think men realise that sex is such a psychological process for women. My DH definitely doesn't even though I've explained it to him a million times! For men, sex can be very emotional and psychological, but I think they can also get turned on so quickly and easily, and can easily separate out the physical from the emotional. E.g. my DH would be miffed when I didn't want to have sex when we'd just finished arguing about house work! The lack of empathy and 'mental foreplay' is just such a turn off for me. Is it the same for you?
I'm also wondering - have you ever experienced pleasure during sex? Have you ever reached orgasm? Is there something, anything, other than your husband that turns you on? Even just a little bit?