It is my understanding that the hormones take up to a year after childbirth to correct themselves, and then after having a baby, birth control becomes an issue again, and birth control pills are well-known to diminish libido in a LOT of women.
To the original poster - I actually find it kind of unbelievable after all this time together, you have no better insight as to what is going on, whether it be related to child-rearing, medication-induced, the onset of menopause, or simply a lack of emotional connection. Really, if it isn't one of those things, I would have to guess that technique is a problem.