Tugging feeling in my lower belly 6-7 days after O

Hi ladies, we've been TTC for almost a year with no luck. Track my O so know when to BD - in my eyes I do everything right. BUT, every month - at about 6-7 days after O - I get this strange tugging feeling in my lower belly (it's quite painful but only for a little while) and I just know straight away that baby failed to "stick" again. It makes me said to think that I can't conceive because of stressful environment at work. Anyone experiences the same thing?