Is it possible to become infertile in only 7years after having your fifth healthy child?

I'm 44 with fsh levels of 3.7. I had my fifth child in October 2009. I have had no problem with getting pregnant in the past, and I'm wondering why it's taking so long this time! All my tests have come back great, my dh is younger than I and has super swimmers!! We're trying clomid for a few cycles, but we really don't want to have too much unnatural intervention. We're both taking supplements to increase fertility,as well as a very healthy lifestyle and diet. I just don't get it. I should be pregnant by now...