Hey S. --
(disclaimer: all my thoughts come from my own experience, and your husband may be nothing like mine. also, we're expecting our first child in March, so my thoughts are also from the pre-parenthood side of the fence. so, take what you want, and leave the rest. :o) )
My husband is a lot less interested in sex when he's stressing out about things, too. Is there any way to address or relieve the causes of his current stress? Is it work/money related? Family/extended family issues? Is he having other worrying health issues?
Would it be possible for you to take up more of the slack, if there is any? Possibly taking a second or part-time job to earn some extra money, looking into a financial education class to help with budgeting issues, arranging your schedules so he can go back to school if he's looking for a career change, spending more (or less ...) time with family members, etc. You may already be overextended (who isn't?) but if it's possible, it might be something to try.
Also, my husband tends to get cranky if he doesn't have some time (an hour or so) by himself every day or two. It seems counter-intuitive to me, but he seems a lot more amorous if he has had sufficient alone time. (I, on the other hand, feel more interested in sex when we've had sufficient time *together*, so ... there you go!) Does your guy need more time by himself?
And finally, do you feel comfortable just asking him "Can we have sex this week? How about Friday (or whenever)?" Sometimes my guy's just kind of clueless and needs me to be more, er, explicit about what I'm wanting or needing. Ultimately, of course, you must find a balance between his and your own sexual (and other) needs, but it's hard to do unless you're upfront about what those needs are.
I wish you the best of luck!