First things first - have you always felt this way about sex? If not, when did you notice your libido starting to dwindle? Can you tie it to an event? Change of job, illness, breavement, stress, etc?
When he wants to have sex, do you turn him down? Do you enjoy sex when you actually do it? I ask because just not being in the mood isn't really a reason to turn him down if you do actually enjoy it once started. So, if you've been turning him down "just because" then stop doing that. I also firmly believe that the more sex youi get the more you want. So use it or lose it.
Next thing - stop thinking along the lines of "we should be doing this". The only people who can know how often you should be having sex are you. There is no national average scale per age. Is he unhappy about not getting sex? Would he want more? Have you asked him? It is VERY important to talk about this (calmly and always outside of the bedroom).
Has he been screened for depression? If not, then I suggest you look into that.
I doubt the pill is at the origin of your lack of libido (seeing as you've been taking it for a long time and it doesn't appear to have affected you in the past) and that your working routine is. If y ou're exhausted then it's only natural that your sex drive diminishes. Sleep and rest are much higher up on the list of human needs than sex. So, if I were you, I'd find a way of working shorter hours and getting more rest. Your sex drive will take a turn for the better and your husband will thank you for it.
Good luck.
There's nothing inherently dirty about sex, but if you try real hard and use your imagination you can overcome that.