How can I have a luteal defect when my progesterone is apparently normal?

[Totesamazeballs]

Hi mumsnetters,

Can anyone help me? I have been tracking my basal temps for the last few months and it appears my LP is 5/6-8 days which is a bit crap for conception.

I have just got the progesterone blood tests back and although I haven't seen the results or spoken to a doc, the receptionist said all normal.

I am thus confused about it all. What else can cause a crappy LP?

Yours, feeling a bit helpless,
Totes x