Hi Neda,
I have mild endo and it took me about 10 months to concieve my son (born in Oct 2010). I fell pregnant in a month that we weren't 'trying' (we were in the middle of an interstate move and thought we had missed the window so were discounting anything happening that month!). Due to us living in different states for most of the month - there was only one date that it could have been - but it was much later in my cycle than i had thought my TTC window was. I have very irregular periods (30-35 day cycle) - but I had accounted for that in what i thought was my prime ovulation days - but obviosuly not enough! So all I can reccomend is trying at lots of different times of the month!
I have been pleasantly suprised (tuoch wood), that since my period has returned I have had relatively pain free periods (where as I had crippling pain before I fell pregnant). So I am hoping this continues.
We have just started TTC again this month - so we'll see what happens this time.
Stay positive and strong and I hope something happens for you soon.