M.I.
Are you temping? I remember reading something about luteal phase defect and low progesterine so I googled it, I need to look into it more too because I've had a bad run with fertility and pregnancy this year. Basically your temp. should rise after you ovulate and your luteal phase should be between 10-14 days. If your temp. isn't high enough and your lp is too short then luteal phase defect may be the culprit. Fertilityfriend.com is a good resource for charting. I've never temped myself, (just bought the thermometer) but I think I may try it. Good luck!
http://www.google.com/search?sourceid=navclient&aq=6&...