Husbands low sex drive?

So, my husband and I have been together for 12 years now and we finally got pregnant back in Oct, 2006 but it ended in a Miscarriage. We have been "trying" to conceive for the past 7/8ish years. My problem is ever since we have been together he has not really been into sex, it has gone from once a week with constant begging to about once every two or three months, because I have just given up on begging. So it is frustrating because I want a baby and he does too, sometimes. So my question is has anyone had this experience and if so how do you handle it? Or, how do I get him more interested or something...

Also our ages are 27 and 30